In 1938, at the naval yards in Galati, Romania, started the construction of two new submarines: S1 and S2. S1, which was renamed NMS Rechinul was launched on 5 May 1941. However it was not yet complete and only on 9 May 1943 entered officially in the ranks of the Navy. Then it had to go through a testing period and was declared ready for action in April 1944.

The first war patrol of NMS Rechinul took place between 20 April – 15 May 1944, under the command of lt. cdor. Corneliu Lungu. Its mission was to observe the activity in the port of Zonguldak, from where almost all ships carrying Turkish coal exports left. Turkey was under pressure from the Allies to join the war on their side. In this case, the Axis submarines and torpedo boats would have been launched an attack against the traffic originating from this port. But because the Allies couldn't offer protection for their coastline, the Turks declined the offer.

On 28 April the submarine received the order to move in the area of the Soviet naval base at Batumi, where it arrived the following day. It was informed that two Soviet cruisers were in the area, but it failed to make contact. On 30 April, at 1546 hours, a patrol aircraft attacked it and, one and a half hours later, two torpedo boats searched for it, without success. On 3 May, at 2035 hours, it had again spotted two ships coming out of the harbor, but lost them in the fog after several hours, so it returned to the designated mission area. On 5 May Rechinul avoided two patrol ships at 2054 hours and the next day a patrol airplane and a patrol boat. The same thing the following days, when the submarine encountered several seaplanes or boats. It was clear that the Soviet anti-submarine defences had grown in number and quality since the time of Delfinul's patrols in 1941 – 1942. By 13 May, the evacuation of Crimea was complete, so there was no need to cover it with the submarines. Rechinul sailed home, via southern Crimea, and arrived in Constanta on 15 May.

The next war patrol was also the last war patrol of a Romanian submarine in WWII. It was also the longest, taking place between 15 June – 29 July 1944. The commander was cpt. Nicolae Turcanu. It was a surveillance mission at Novorosiysk. On 18 July the submarine arrived in the designated area of operations, taking up positions near Cape Utrish, Northwest of the port. The following day, around 1420 hours, it avoided a seaplane and on 25 June two patrol ships. Thus, cpt. Turcanu decided to go Southwest of Novorosiisk, in the area of Cape Idokopass. On 27 June, it noticed two torpedo boats at 1053 hours and, five hours later, several explosions were heard in the distance. The following morning, around 0330 hours, two submarine hunters appeared in the area and, at 0500, launched the first depth charges. There were 16 in total, of which 4 fell close to the submarine, causing minor damages. On 1 July it went back to Cape Utrish, but on 4 it was again at Idokopass. It was searched for and attacked between 0135 and 0730 hours. Two days later, explosions were heard further away and Rechinul moved to the area of Cape Utrish, where it remained until 10 July, when it again changed position. It repeated the maneuver on 16 July and then on 18. This frequent change of area of operations prevented the ChF from locating it. On 18 July it was at Cape Idokopass, when it was finally found and the following day was attacked with 38 depth charges between 0335 and 0410 hours. Thus, on 20 July the submarine headed North, where it was again discovered on 23. The next day it was hunted from 0920 to 1225 hours and the crew counted 43 explosions, out of which 2 very close. On 27 July it received the order to return home and arrived at Constanta after two days.

Specifications

Crew	45
Displacement on surface	585t
Displacement in imersion	680t
Length	58m
Width	5.6m
Draft	3.6m
Max speed on surface	17 knots
Max speed in imersion	9 knots
Range	7000 miles
Guns	1 x 88mm
Machineguns	1 x 20mm
Torpedo tubes	6 (4+2) x 533mm