Căpitan (USN rank - lieutenant) Constantin Costăchescu commanded "Delfinul" on its first war patrol which lasted 22–27 June 1941. A simple reconnaissance mission from shore. On 26 June at 00:30, Costăchescu reported back to Constanța that a large Soviet war group was approaching Constanța. Because they lost their element of surprise, the Soviets lost a destroyer ("Moskva") and the lead ship "Kharkov" and the cruiser "Voroshilov" were damaged in the following battle.