By the ship's fifth voyage, Izac was its executive officer. During this voyage, the ship successfully ferried troops to Brest, France on May 23, 1918 and began the return trip to New York City on May 29. The next day, the destroyer escort for the convoy departed, leaving four troopships to cross the sea alone. Izac was in command of the guns on the afterdeck. A submarine was spotted early in the morning on May 31 and the ships attempted to evade it unsuccessfully. "President Lincoln" was with a convoy of ships from the coast of France when it was struck by three torpedoes at a range of about at 08:54 by German submarine . By 09:15, her captain, Commander P.W. Foote ordered the ship abandoned. "President Lincoln" rolled starboard at 09:30 and sank, but only took 26 men in a crew of 700 with her. The rest remained in lifeboats as the rest of the convoy headed to a safe distance, as was policy at the time. "U-90" then surfaced, attempting to locate the ship's captain, but was unable to do so, pulling Izac out of a lifeboat instead because its crew recognized his officers' insignia. Izac was taken as a prisoner of war after lying to the sub's crew that the captain had gone down with the ship. He was subsequently held in quarters aboard the ship while it dived to avoid depth charges from the pursuing .