During salvage in the aftermath of the West Loch Disaster, he lost his life in a rescue operation at Pearl Harbor on February 17, 1945.

In 2021, VFW Post 3720 in Swartz Creek was renamed the Francis P. Hammerberg Memorial Post Hammerberg's official Medal of Honor citation reads: For conspicuous gallantry and intrepidity at the risk of his life above and beyond the call of duty as a diver engaged in rescue operations at West Loch, Pearl Harbor, 17 February 1945.

Hammerberg unhesitatingly went overboard in a valiant attempt to effect their rescue despite the certain hazard of additional cave-ins and the risk of fouling his lifeline on jagged pieces of steel imbedded in the shifting mud.

Wearied but undaunted after several hours of arduous labor, Hammerberg resolved to continue his struggle to wash through the oozing submarine, subterranean mud in a determined effort to save the second diver.

Although he succumbed in agony 18 hours after he had gone to the aid of his fellow divers, Hammerberg, by his cool judgment, unfaltering professional skill and consistent disregard of all personal danger in the face of tremendous odds, had contributed effectively to the saving of his 2 comrades.