Upon the entry of the United States in World War I, he was appointed acting chaplain with the rank of lieutenant junior grade and assigned to the 11th Marine Regiment in France, where he served until 1919.

Rentz was a crew favorite, even going so far as to ignore regulations and dispense nips of alcohol as needed to the exhausted sailors.

[1] During a Japanese attack on Houston at the Battle of Makassar Strait on February 4, 1942, Commander Rentz spurned cover and circulated among the crew of the anti-aircraft battery, keeping up their spirits.

Less than a month later, Houston and the Australian light cruiser HMAS Perth (D29) were directed to proceed to the Dutch East Indies port of Surabaya, where they were supposed to attack Japanese naval supply lines.

In the ensuing melee one of the Japanese destroyers fired a spread of torpedoes that passed by the allied cruisers and sunk four of their own troopships.

It was during the abandonment of the sinking Houston that Commander Rentz entered the water and attained partial safety along with other crewmembers on a destroyed airplane's float.

Seeing extreme overcrowding and the fact that the pontoon was taking on water, he attempted to relinquish his space and lifejacket to wounded survivors nearby.