On November 14, 1939, as World War II raged on, the Kriegsmarine placed an additional order for its Schnellboot torpedo boats. The vessels were all identical in design to the pre-war S-30 class, featuring shortened, narrowed hulls and MB502 engines. A total of eight boats were ordered and designated S-54 through S-61. Like most Schnellboots, the S-61 was built at the Lürssen shipyard in Bremen. It was launched on November 27, 1940, and commissioned on February 1, 1941.

It spent most of its service in the Mediterranean Sea, fighting against Allied ships. On September 8, 1943, the S-61 and the S-54 were in Taranto and found themselves in a difficult situation. Italy had surrendered, and the port was to be handed over to the Allies. That evening, the boats laid mines that struck the high-speed minesweeper HMS Abdiel the next day, killing a potion of the crew and over 100 soldiers. On September 11, the boats encountered and sank the Italian gunboat Aurora. At 4:50 p.m., they encountered an Italian transport ship that surrendered and was sent to Venice. Then, at 5:45 p.m., they encountered the Italian destroyer Quintino Sella, which was en route to surrender to the British. The Quintino Sella was hit by two torpedoes and sank. That evening, the S-54 and the S-61 arrived in Venice, where they participated in capturing the city and disarming the local garrison. The remainder of the S-61’s service passed without incident. However, sources differ on how it was lost. One account states that it collided with the S-36 on February 6, 1945. Another account states that it raised white flags and surrendered at Ancona on May 3.

The S-61 was introduced in Update 2.55 "Ninth Wave". It is one of the oldest designs in the class, which is why it is smaller and has a smaller crew. Survivability is worsened by the fact it only has one, albeit powerful gun. The loss of it leaves the boat only with torpedoes. Like other S-boats, it boasts good speed.