NMS Delfinul (The Dolphin) was a Romanian submarine that served in the Black Sea during the Second World War.

[1] Delfinul was ordered in 1927 from the Italian naval base and shipyard at Fiume (today Rijeka, Croatia).

When Romania entered the war (22 June 1941), the navy had only one submarine, but that presence meant that the Soviet Black Sea Fleet had to secure an anti-submarine service for its convoys and near its naval bases.

Căpitan (USN rank - lieutenant) Constantin Costăchescu commanded Delfinul on its first war patrol from 22 – 27 June 1941.. A simple reconnaissance mission 60 nautical miles (111 km; 69 mi) from shore.

The next patrol took place from 10 to 20 July, under the command of Căpitan (USN rank - Lieutenant) Corneliu Lungu.

Delfinul patrolled the south of the Crimean peninsula and made a reconnaissance mission to Novorossiysk, trying to evaluate the anti-aircraft and anti-submarine capabilities of the enemy naval base.

During the night, it was detected by an enemy patrol craft, but Delfinul quickly submerged and avoided being attacked.

95 nautical miles (176 km; 109 mi) from Cape Sabla, Delfinul spotted a small Russian submarine on the surface, probably from the Malyutka class.

Delfinul tried to attack it with the deck gun, but the rough seas and two unidentified hydroplanes led the commanding officer to decide to dive the submarine and break contact.

Delfinul swiftly counterattacked with her twin 13mm machine gun, causing the Soviet submarine to submerge and retreat.

On 10 September, the submarine got into firing range of a two-ship convoy 20 nautical miles (37 km; 23 mi) west of Cape Otrishenok, but the charge of an escort vessel forced Căpitan Lungu to submerge and lose contact.

On 17 September, it took a course for Constanța, and, on the way back, it was spotted by several Russian hydroplanes and even depth charged by a patrol craft.

Căpitan (USN rank - Lieutenant) Constantin Costăchescu was later awarded the Order of Michael the Brave 3rd Class for the attack.

[8][9] However, according to modern evaluations, the ship was sunk by the Luftwaffe on 30 October, during an air raid on Yevpatoria, and the torpedo attack missed the minelayer Ostrovsky [10][self-published source?

][11] The latter claim, however, is highly unlikely, as the crew of Delfinul reported to have heard an explosion seconds after launching the torpedo.

Delfinul left port on the 30 November, but because of bad weather, it was forced to return to base on the 3 December 1941.

After 16:00 (4:00 pm), an enemy patrol craft appeared, and Căpitan (USN rank - Lieutenant) Costăchescu ordered a complete stop on the electric motors.

On 1 July, the last day of the Sevastopol evacuation, the Russian flotilla was very active in the Crimean zone, so Delfinul was spotted and hunted for 13 hours.

The Romanian Submarine Service had its motto as the Latin expression: Audaces Fortuna Juvat, which means "Fortune favors the bold" (rom.-"Norocul îi ajută pe cei îndrăzneți").