Two Towers

Loading a torpedo aboard the Greek submarine Xifias in Toulon, France. It was a sister ship of the submarine Delfin, mentioned in the article. Photo: Galica

Text: Petr Uzsák

At the outset, I would like to apologise to readers for the misleading title, which may suggest a connection with the work of the famous J. R. R. Tolkien, when in fact the opposite is true. This text will not draw on the realm of fantasy, as it focuses on specific historical facts of naval warfare.

Greece's submarine force is not particularly well known to the general public, but its history includes several remarkable episodes. Few people know, for example, that as early as 1912 the Greek submarine Delfin attacked the Ottoman light cruiser Macidiye, albeit unsuccessfully. Nevertheless, it was the first underwater torpedo attack in military history.

Today, two preserved conning towers of Greek submarines can be seen in Athens—which explains the title. The first comes from the pre-WWI vessel Y-2 Papanikolis and is held in the collection of the Piraeus Maritime Museum. The second artefact mentioned is the conning tower of the submarine Y/B S118 Okeanos. It stands in Flisvos Park in the Palaio Faliro district and represents the post-WWI German school of submarine design.

Y 2 Papanikolis

In the mid-1920s, the Greek monarchy ordered the construction of two submarines in France, its first submarine order since the end of the Great War (now known as the First World War). As noted, the order comprised two vessels. We will focus on the one designated Y 2 Papanikolis, whose sister ship was designated Y 1 Katsonis.

Construction of the submarine Papanikolis began at the Chantiers de la Loire shipyard in Nantes in 1925. It was a conventional diesel-electric design of the Schneider–Laubeuf type. It was not an entirely new project, but a design derived from the French Circé class. The boat was completed in 1927 and was accepted and commissioned by the Hellenic Navy in December of that year. To be precise, this took place at 2:45 p.m. on Wednesday, 21 December 1927, in the port of Toulon. The very next day, the crew conducted an acceptance trial that included a practice torpedo launch and a test firing of the deck gun. Its first commanding officer was Commander (Cdr) Panagiotis Vandoros.

Two days later, on the afternoon of 24 December 1927, the boat weighed anchor and departed Toulon for Greece. It arrived five days later, on the afternoon of 29 December, where it received a ceremonial welcome. It then moored at its assigned berth, Buoy No. 8 at Salamina Naval Base.

Painting the deck guns of the submarine Papanicolis. The photograph was taken in Beirut, Syria, between 30 October and 7 November 1942. Photo: IWM

The boat's mission was coastal defence, as it had not been designed for extended ocean-going deployments. Its range was 3,500 nautical miles (approximately 6,500 km), which was nevertheless entirely adequate for Mediterranean conditions.

Its principal technical specifications were as follows: length 62.5 m; beam 5.3 m; draught 3.6 m; full displacement 605 tonnes surfaced and 787 tonnes submerged. Propulsion was provided by diesel engines with a combined output of 970 kW and electric motors rated at 750 kW. Driving two propellers, they could give the boat a speed of 14 knots on the surface (25 km/h) and 9 knots submerged (16 km/h). The armament comprised two internal bow torpedo tubes of 533 mm calibre, two external bow torpedo tubes of the same calibre, two external stern torpedo tubes also of 533 mm calibre, and a 100 mm deck gun. The crew consisted of six officers and 39 petty officers and sailors.

After acceptance by the navy, the vessel and its crew carried out routine peacetime duties involving training, maintenance and visits to various Greek towns and islands. In 1929, for example, the submarine visited the islands of Corfu and Lefkada as well as the port of Patras. The following year it returned to Lefkada and Corfu and also visited Ithaca (made famous by the Homeric hero Odysseus) and Zakynthos.

Everything changed in the autumn of 1939, by which time independent Poland had been destroyed and the Soviet Union had just attacked Finland. It was becoming clear that peace in Europe was over, and the crew of Papanikolis also began preparing for war. It should be stressed that the Greek submarine force was not in the best condition, primarily because of financial constraints and their impact on equipment maintenance. But that was soon to change.

Dimitrios Papanikolis was a hero of the Greek national liberation struggle and War of Independence, and later an admiral and politician. He lived from 1790 to 1855 and came from the island of Psara in the Aegean Sea. He became famous for his fight against the Ottoman Empire and his innovative naval tactics. A Hellenic Navy submarine is still named after him today, namely a Type 214 boat.

Photo: National Historical Museum of Greece

The Greco-Italian War broke out on 28 October 1940. At that time, the submarine was commanded by Lieutenant Commander (LtCdr, equivalent to a major in the army) Miltiadis Iatridis, and its task was to operate in the Ionian Sea. During this war, Papanikolis completed a total of five war patrols and sank two Italian vessels.

After Nazi Germany invaded the Kingdom of Greece and occupied the Greek mainland, the submarine's crew managed to sail to Alexandria in Egypt. There it became part of the British 1st Submarine Flotilla.

The submarine subsequently joined the Allied war effort and conducted further war patrols in the Mediterranean. Their objectives were to attack shipping or transport Allied agents and special forces to occupied territories. During these operations, it sank more than 13,000 tonnes of enemy shipping. This was achieved despite the limitations imposed by its technical condition: for example, the submarine could not remain submerged for long and had to surface every 17–18 hours to replenish its air supply.

Most of Greece was liberated in October 1944. At the time, Papanikolis was in Malta undergoing further repairs to its propulsion system. The boat returned home on 24 November 1944.

At the time of Greece's liberation, it was one of only two submarines—from a pre-war total of six—to survive the Second World War. The other was Y 4 Nereus, which was decommissioned in 1947.

By the end of the war, the submarine had completed 18 years of intensive service, and its technical condition and performance had long since ceased to rank among the best. Wear to the propulsion system, which had already caused problems before the war, was a particular concern. In July 1945, a decision was therefore made to retire the boat because it was obsolete. In recognition of its achievements, the vessel's conning tower was removed and respectfully preserved, while the hull was sold for scrap and dismantled in 1947. In addition to the complete conning tower of Papanikolis, the museum's collection also contains torpedo tubes, the complete periscope and a compass mount. The Athens War Museum displays an original British-made Model 1937 torpedo dating from the Second World War.

The boat exemplifies the Greek war effort and the seamanship required to operate an obsolete vessel, and it certainly deserves its place in Greek history.

The Peruvian submarine BAP Pisagua (SS-33) is a German Type 209/1200 vessel, a type that also includes the Greek submarine Y/B S118 Okeanos. Photo: US Navy

Overview of war patrols:

1st war patrol: 28 October–2 November 1940, Ionian Sea area, commanding officer: LtCdr Miltiadis Iatridis. The submarine departed Salamina Base in the afternoon together with the submarine Y 4 Nereus. The following morning, the boats reached the port of Patras. There, after some minor organisational confusion partly caused by Italian aerial bombing, arrangements were made for cooperation with the British Navy and operating areas were assigned. In the afternoon, the submarine sailed on patrol into the Gulf of Patras, from where it moved after dark to the strait between the island of Kefalonia and the mainland port of Kyllini. The next evening, 30 October, while patrolling between Zakynthos and Kefalonia, the submarine's crew sighted unidentified vessels that they assumed were British. It therefore left the area without taking further action. Shortly before noon the following day, the hydrophones reported an approaching target. Because of the dense fog, its identity was initially unclear. It was soon confirmed, however, that the contacts were Greek Hydra-class destroyers: Psara and Spetsai, returning from shelling Italian ground forces on the Greek-Albanian border. The patrol ended on the morning of 2 November because of numerous mechanical failures in onboard equipment, including the rudder, compass and water pumps.

2nd war patrol: 17–27 December 1940, Adriatic Sea area, commanding officer: LtCdr Miltiadis Iatridis.

The submarine departed the port of Salamina shortly before midnight and reached its assigned area on the morning of 20 December. The delay was caused by stormy weather. Shortly after midnight on 22 December, while travelling on the surface, the submarine detected the small coastal steamer Antoinetta from Salerno, Italy. After a concealed approach, the vessel, which was carrying livestock fodder, was quickly captured. Its crew were transferred aboard the submarine, which they believed to be British. The Italians could not believe that the Greeks had submarines operating in the Adriatic. The Greek crew first tried to sink the steamer by ramming it and later by setting its cargo on fire. The prisoners provided the Greeks with maps of Italian minefields in the Adriatic and information about a convoy scheduled to sail the following day from Brindisi to Vlorë, Albania. The submarine was operating in this area and, on the afternoon of the next day, located enemy transport vessels escorted by destroyers. A Zara-class cruiser was also sighted. Stormy weather, however, made it impossible to approach and attack. On 24 December, by contrast, the crew had better luck. It spotted a convoy of 12 transport vessels sailing in three columns and escorted by at least six destroyers, with numerous Italian aircraft providing air cover. After approaching the convoy, the boat fired a salvo of four torpedoes at 12:24 p.m. and immediately began withdrawing from the enemy. Within a few minutes, however, the Italian escorts recovered and attacked the submarine for several hours. Only at 9:30 that evening did the crew dare to surface and head south. The following afternoon, while travelling at periscope depth, the boat was attacked by an aircraft that dropped several bombs. Fortunately, they did not damage Papanikolis. On the way back to base, the boat made a brief stop at the port of Isthmia on the eastern side of the Corinth Canal, where the police took custody of the submarine's prisoners. It then continued directly to Salamina Base, where it moored on the morning of 27 December.

It was later confirmed that the submarine had sunk the large troop transport Firenze. For this success, the boat's commanding officer was promoted to Commander (equivalent to a lieutenant colonel in the army) and awarded the Gold Medal for Valour. Other crew members were decorated with War Crosses, and the story was reported throughout the Greek media.

The preserved conning tower of the submarine Papanikolis in the outdoor exhibition of the Piraeus Maritime Museum.

3rd war patrol: 23 January–1 February 1941, Adriatic Sea area, commanding officer: Cdr Miltiadis Iatridis.

On the afternoon of 23 January, the boat departed Salamina Base westwards on another patrol. At midnight on 24/25 January, near the island of Ithaca, it met the submarine Y 4 Nereus, which was returning from patrol. The commanding officers exchanged experiences, and on 26 January Papanikolis continued north into the Adriatic. On the way, the submarine was detected several times by Italian vessels and aircraft, but fortunately all their attacks were unsuccessful. The boat also sighted several Italian transport vessels but was unable to attain a suitable attack position. It was not until midnight on 28/29 January, while cruising on the surface in the Brindisi area, that the crew spotted a large cargo ship with an armed escort at a distance of approximately 800 metres. The submarine fired one torpedo and disengaged from the enemy. Although the crew subsequently sighted Italian vessels several more times, the submarine came under no further attack and returned to Salamina Base on 1 February.

Subsequent analysis did not confirm that any Italian vessel had been hit during this patrol. After returning, the commanding officer also emphasised the difficult conditions for submarine operations caused by Italian patrols.

4th war patrol: 1–6 March 1941, Adriatic Sea area, commanding officer: Cdr Miltiadis Iatridis.

The boat departed on its next patrol on the afternoon of 1 March 1941, once again heading for the Adriatic. The initial phase, during which the submarine operated near the Albanian port of Vlorë, was beset by several technical failures that led to a partially flooded the battery compartment. Acid fumes began to escape from the batteries, forcing the boat to surface. It had to remain on the surface while the water was pumped out, the faults were repaired and the boat was ventilated. The commanding officer therefore ordered the boat to proceed south on the surface at full speed and simultaneously called the gun crew to the deck, where they stood ready for action. After two hours, most of the damage had been remedied and the submarine was able to take shelter beneath the surface. Nevertheless, poisonous fumes continued to escape, leading the commanding officer to terminate the patrol and return to base. Headquarters approved his decision, and the boat moored at Salamina Base on the morning of 6 March.

5th war patrol: 14–19 April 1941, Adriatic Sea area, commanding officer: Cdr Miltiadis Iatridis.

The submarine departed Salamina Base once again on 14 April for its next patrol. To provide the full context, by then Greece was already under German attack, which had begun eight days earlier. The commanding officer was advised that, if a return to the home port proved impossible, the submarine would be sent to the British base at Alexandria in Egypt.

After three days at sea, the commanding officer was instructed to proceed immediately to Alexandria because of the continuing German advance. Nevertheless, Iatridis requested permission to return to the home base for essential repairs, and permission was granted. The boat returned to Salamina on the evening of 19 April, and work to rectify the defects began immediately.

On 22 April, in accordance with its previous orders, it departed for Alexandria, arriving on 27 April 1941. Beforehand, the boat made a brief stop at the Greek base at Souda on Crete.

At Alexandria, the submarine underwent essential repairs to prepare it for the next phase of the war.

Side view of the conning tower of the submarine Papanikolis. Note the 100 mm deck gun and the preserved torpedo tube in the foreground.

6th war patrol: 4–17 July 1941, Mediterranean Sea area, commanding officer: Cdr Miltiadis Iatridis.

The boat was sent from Alexandria Base to the area around the island of Kastellorizo in the Eastern Mediterranean, with orders to attack enemy convoys heading for Syria and Palestine. Although the submarine sighted several vessels, checks showed them to be Turkish, so no attack was made. Owing to continuing technical failures, the boat achieved no successes and returned to base.

7th war patrol: 6–20 June 1942, Aegean Sea area, commanding officer: Cdr Athanasios Spanidis.

After several months of repairs in Alexandria and Port Said, the submarine was once again ready for action. In the meantime, there had also been several changes of commanding officer. The officer of greatest interest to us is Commander Athanasios Spanidis, who was appointed to the post in April 1942.

The boat left Alexandria Base on the evening of 6 June with orders to patrol the area between the Peloponnese coast and Crete, in the south-western part of the Aegean Sea. Its mission also included landing members of the Greek resistance movement on occupied Crete, while the submarine picked up a group of Allied commandos there.

Its first success came on 11 June with the sinking of a cargo sailing vessel in enemy service. To conserve valuable torpedoes and artillery shells, the small craft was destroyed by ramming. The following day brought further prizes: first, two sailing vessels were sunk, the larger by gunfire and the smaller by a blow from the submarine's bow. Later that same day, a cargo sailing vessel carrying fuel was sunk, and in the evening the submarine destroyed another sailing vessel carrying salt.

Two days later, the crew accomplished a daring feat. The commanding officer sent a boarding party in a boat to a cargo sailing vessel in the service of the occupiers, anchored near Porto Cayo. The party seized the guarded vessel and sailed it out to sea, where the submarine promptly sank it by ramming. It was discovered that the cargo consisted of many tonnes of food intended for German garrisons in Greek territory.

On the night of 15/16 June, the submarine covertly landed resistance fighters on the Cretan coast and evacuated Allied troops from there. It returned to Alexandria on 20 June after a dangerous voyage through enemy waters.

8th war patrol: 24 July–9 August 1942, Crete area, commanding officer: Cdr Athanasios Spanidis.

On the evening of 24 July, the submarine sailed from Haifa on a special mission. The change of home port was prompted by a major Axis offensive that directly threatened Alexandria and other parts of Egypt. The boat's mission was to transport members of the resistance movement and British officers to the southern coast of Crete; in fact, it was carrying two separate groups.

During the voyage, the submarine encountered bad weather that nearly made the landing operation impossible. At first, communications with the reception party on Crete also failed. Fortunately, the problems were gradually resolved. During the first part of the operation, the submarine landed 17 Greek resistance fighters and one British officer, while taking aboard a group of 24 Greeks and another British officer. In his memoirs, one of the Greek resistance fighters ashore describes this landing from their perspective (George Psychoundakis, The Cretan Runner).

The second part of the mission, however, was not completed and no landing took place, as contact with the shore could not be established and the site instead appeared to be under the occupiers' control. All this occurred during the night and early morning of 4 August.

Another notable aspect of the mission was the evacuation of a leading resistance figure, Lieutenant Colonel Andreas Papadakis, his wife and their three children. All were transported beyond the reach of German forces to the Allies.

On the return voyage, the submarine reported that it was short of fuel and requested assistance. Thanks to the prompt intervention of the destroyer Kountouriotis, it was refuelled, and on the evening of 9 August the submarine moored in the port of Beirut.

Detail of the preserved torpedo tube.

9th war patrol: 31 August–15 September 1942, Rhodes area, commanding officer: Cdr Athanasios Spanidis.

For its next mission, the submarine was dispatched from Beirut at the end of August, again to covertly transport a group of commandos and their equipment. This time the boat headed for the island of Rhodes, and there was no shortage of dramatic moments. On 2 September, while cruising on the surface, the submarine came under machine-gun fire from an Italian patrol aircraft. As Papanikolis could not dive immediately, it made an unsuccessful attempt to return fire. The same day, the submarine encountered an enemy tanker escorted by two corvettes. The attack failed, however, because of the considerable distance and the evasive manoeuvres of the targeted vessels.

The boat reached the coast of Rhodes on the evening of 4 September. During the night, it landed Allied soldiers tasked with attacking German and Italian aircraft on the island. In return, another group of commandos who had been operating there covertly was evacuated from the island during the operation.

The submarine returned to Beirut on 15 September. There, its commanding officer, Spanidis, had to answer criticism from his superiors over his poor handling of the crew, which ultimately resulted in his dismissal.

Incidentally, the commandos' attack on the airfield was highly successful, but only a few individuals made it back to the Allies; the rest of the group were captured.

10th war patrol: 21 November–5 December 1942, Aegean Sea area, commanding officer: Lt Nikolaos Roussen.

The boat did not set out on its next patrol until November, this time under a new commanding officer, N. Roussen. He had assumed command at the beginning of October, and both the executive officer and the engineering officer had also been replaced. The crew had two principal tasks: to land a group of resistance fighters on Crete, and then to patrol the eastern Aegean and attack enemy transport vessels.

The first part of the mission was completed on the night of 27/28 November, when a group of resistance fighters and their equipment were landed in Selino Bay on the south-west coast of Crete. The aforementioned G. Psychoundakis adds that on this occasion no one was waiting for the group ashore and, moreover, some of the equipment sank in the sea because of the bad weather. Once the resistance fighters had made contact with local people, they returned to the coast the following night and recovered their equipment.

Meanwhile, Papanikolis continued its patrol. On 30 November, the crew located an anchorage used by enemy vessels off the island of Alimia, west of Rhodes. The group comprised several torpedo craft and a sailing vessel, but above all a transport steamer with an estimated displacement of 8,000 tonnes. Before dusk the following day, the submarine cautiously entered the bay and fired two torpedoes at the transport from its stern tubes. Shortly after the attack, the steamer capsized and sank. Meanwhile, the submarine disengaged and sailed north.

It returned to its Beirut base on 5 December. The crew was also decorated for this action: the commanding officer received the War Cross, 1st Class, and other crew members were similarly honoured.

Technical problems again made themselves felt during this patrol, including failures of the port diesel engine's cooling system and the ballast-water pump.

The original periscope of the submarine Papanikolis in the museum's collection.

11th war patrol: 7–23 January 1943, Aegean Sea area, commanding officer: Lt Nikolaos Roussen.

On the afternoon of 7 January, Papanikolis once again left Beirut, heading for the island of Hydra off the eastern coast of the Peloponnese. This time, too, it carried a group of commandos who were to be landed on the island.

Apart from stormy winter weather, the voyage was uneventful. Nevertheless, the submarine reached its destination, and in the evening darkness of 13 January the unit and its equipment began to disembark. Everything was completed within two hours, and the boat departed once more. Its next objective was to disrupt enemy supply and minesweeping operations in the Aegean. Shortly after noon on 17 January, the boat sighted and detained a two-masted sailing vessel carrying food for the German garrison on Crete. A British prize crew transferred to the sailing vessel and was ordered to sail east to Alexandria.

The following day, another sailing vessel was detained, this one carrying raisins and also bound for Crete. After warning shots from the gun, the vessel stopped and lowered its sails. A short while later it was sunk by machine-gun fire from the submarine, while the sailors were interrogated. Papanikolis then submerged again and continued eastwards.

Shortly afterwards, the patrol had to be terminated because numerous technical failures prevented the boat from diving, and assistance was requested. It was soon provided by the British corvette K-22 Gloxinia, which escorted the submarine to Port Said. It moored there on the morning of 23 January.

The crew was decorated for this patrol as well, while the boat once again entered dry dock for repairs.

12th war patrol: 7–23 March 1943, Aegean Sea area, commanding officer: Lt Nikolaos Roussen.

On the afternoon of 7 March, the submarine cast off from the support ship Corinthia in Beirut harbour and sailed towards the Dodecanese Islands in the eastern Aegean. This patrol, too, was filled with intense activity.

On the morning of 14 March, the submarine sighted a large steamer, but on approaching it identified the vessel as a hospital ship heading for Rhodes. Papanikolis therefore withdrew without taking further action. The following day, 15 March, it encountered a two-masted sailing vessel. A British boarding party and the submarine's fourth officer were sent aboard with the aim of taking the vessel to Egypt. Unfortunately, two enemy torpedo boats later appeared and escorted the sailing vessel to occupied Rhodes. The Allied soldiers aboard were captured, for which the submarine's commanding officer blamed himself deeply.

On 16 March, a transport vessel was detained, but was released again after it was found to belong to neutral Turkey. That evening, a small Italian sailing vessel bound for Rhodes was stopped and then sunk. Three members of its crew were captured and transferred aboard the submarine. A similar action was repeated on 18 March, and once again captured crew members were carried away by the submarine.

The patrol ended on the morning of 23 March, when the submarine moored at its base in Beirut after once again having to cross a belt of stormy weather.

A British Model 1937 torpedo preserved at the Athens War Museum.

13th war patrol: 30 April–13 May 1943, Aegean Sea area, commanding officer: Lt Nikolaos Roussen.

At the end of April, the boat once again departed Beirut Base for occupied Crete. On the evening of 7 May, it came ashore near Cape Sidero and landed a total of eight people together with supplies for the resistance movement.

The following day, Papanikolis detained a sailing vessel carrying cement to Heraklion, Crete. The vessel was sunk by machine-gun fire, and its crew were detained aboard the submarine. Later that same day, another cargo sailing vessel was sighted and sunk; it too was carrying cement and other supplies for the occupying forces in Heraklion. It went down after being struck by the submarine's bow, and its crew were taken prisoner like their counterparts before them.

Because of a pump failure, the submarine had to break off its patrol on 9 May and sail to Port Said for repairs. It moored there on the morning of 13 May.

Owing to persistent technical problems and a shortage of spare parts, the submarine was used only as a training vessel during the period that followed.

14th war patrol: 29 January–12 February 1944, Aegean Sea area, commanding officer: Lt Nikolaos Roussen.

On the afternoon of 29 January, the submarine departed Beirut with orders to patrol the central Aegean. During the passage to its operating area, the boat encountered a winter storm. Heavy seas caused acid to leak from the batteries and water to enter the hull. After surfacing and ventilating the interior, the damage was repaired and the submarine continued its voyage.

On the evening of 2 February, the lookout aboard the surfaced submarine spotted an unidentified four-engined aircraft, and the boat dived rapidly. This occurred in the strait between the islands of Crete and Kasos.

From 3 to 12 February, the boat patrolled its assigned area, but nothing unusual was observed, so the patrol ended with its return to Beirut. Towards the end of the voyage, the commanding officer fell ill and the executive officer temporarily took command of the boat.

Owing to its technical condition, no further war patrol was planned for the time being. Instead, it was decided to transfer the submarine to Gibraltar for repairs. It was dispatched there on 19 May 1944, but before that the naval command had to deal with a mutiny by part of the crew, which also cost the life of its commanding officer, N. Roussen. He was killed during the intervention against the mutineers as the submarine was retaken by force. Lt Christos Botsaris became the new commanding officer. By then, the submarine was no longer operationally deployed and participated only in training the crews of surface ships and aircraft.

The original preserved conning tower of the submarine Okeanos, rear view.

Y/B S118 Okeanos

This boat belongs to the Type 209 class, designed by the German company Ingenieurkontor Lübeck and built at the Howaldtswerke-Deutsche Werft shipyard in Kiel. In many respects, however, the vessel drew on the preceding Type 206 class. Together with three other units, Okeanos formed part of the Greek Poseidon class. It is also the first vessel in the Hellenic Navy to bear this name. It should be stressed that this type was intended primarily for service in coastal waters.

The vessel was completed and accepted by the navy in Kiel on 15 November 1979, with Lieutenant Commander (LtCdr) Vasilios Morakis appointed as its first commanding officer. Sea trials in the Baltic followed during November and December. The crew began the homeward voyage on 10 December and reached its destination, Salamina Naval Base, on 1 January 1980.

Its principal tactical and technical specifications are as follows: length 55.90 m; beam 6.3 m; submerged displacement 1,285 tonnes; range up to 11,000 nautical miles (20,000 km). The boat has diesel-electric propulsion and can reach a speed of 11 knots on the surface (20 km/h) or 21 knots submerged (39 km/h). Its armament comprises eight 533 mm bow torpedo tubes capable of launching both conventional torpedoes and Harpoon anti-ship missiles. It has a crew of 33.

The boat's active service began immediately upon its arrival. It consisted of routine training and maintenance, and naturally included exercises, both domestic and international (including, for example, the periodic Trident and Dogfish  exercises).

Probably the most dramatic voyage undertaken by Okeanos took place in March and April 1987 during the so-called “March 1987 Crisis.” At the time, Turkey decided to send a vessel to survey fossil-fuel deposits in international waters within Greece's economic zone, claiming that the area formed part of the Turkish continental shelf. It was simultaneously announced that any Greek action against the vessel would be regarded as grounds for war.

At the time, the submarine was commanded by LtCdr Nikolaos Koutsodontis. On 27 March 1987, the boat was sent on patrol in the Aegean after the naval command ordered all vessels to leave their bases and move to designated areas to monitor and, if necessary, block Turkish activities. The crisis was ultimately resolved through diplomatic means with the involvement of the United States and NATO, and fortunately no armed conflict occurred. The voyage lasted 240 hours, and the boat spent most of that time submerged.

Okeanos was an ancient Greek deity of the first generation of Titans, the ancestor of all gods and of humankind. He ruled the river of the same name, which was believed to feed all seas and rivers. He is usually depicted as a muscular man with a serpent's body in place of legs. Tritons and nymphs accompanied him on his journeys.

Photo: QuartierLatin1968

In 2004, under the Neptune II programme and on the basis of a decision taken in 2002, the boat underwent a modernisation conversion. This included the installation of an air-independent propulsion (AIP) system and the modernisation of the existing propulsion machinery and numerous other onboard systems. The purpose was to improve the boat's operational capabilities and reduce its acoustic signature. Another important alteration was the modification of the deck hatch to permit connection to a Deep Submergence Rescue Vehicle (DSRV).

The submarine returned to service in 2009 and is currently the sole representative of the Okeanos class. Budget constraints resulting from the financial crisis at the time meant that the other boats were not modernised.

During the conversion, the boat's original conning tower was removed and later installed in Flisvos Park. With its new sail, the vessel now resembles the Papanikolis class in appearance. Its dimensions also changed: the hull was lengthened, thereby increasing displacement. The boat's performance improved as well. This transformed it into an ocean-going type capable of extended operations without resupply.

Together with the Poseidon- and Papanikolis-class boats, Okeanos is a core element of the Hellenic Navy's submarine fleet, which protects the mainland coastline, more than 2,000 islands and the maritime lines of communication between them.

The original conning tower of the submarine Okeanos from before the vessel's modernisation.