I just had to look it up:
PACKARD V-12 MARINE ENGINE
The Packard 4M-2500 engine was utilized in all U.S. Navy World War II PT boats. This engine was based on the 1925 Liberty aircraft engine which was earlier converted for marine use in racing boats. During the war the Packard engine went through various performance updates and modifications. With early engines rated at 1100 h.p. and progressing to 1500 h.p. during the war. The Packard 4M-2500 engine was a supercharged, water cooled, gasoline powered V-12 engine, weighing approximately 2900 pounds.
The Packard 4M-2500 marine engine was not the Rolls-Royce Merlin, nor did U.S. Navy PT boats use the R.R. Merlin engines, which is sometimes misstated. However, Packard did built a version of Merlin Engine under contract by Britain for British aircraft use.
Several years ago, I was at the NOLA WW2 museum where a Higgins PT boat was being reconstructed. I asked about the hull planking, thinking that it was made from plywood as we know it today.
Actually, the hull was made from mahogany planks in two layers. Higgins owned considerable acreage in the Phillipines, from where came the wood. He had his own sawmills to make the lumber for the boat construction.
The boat has since been completed and now runs around Lake Pontchartrain.
Here’s a piece that details the construction.
https://www.militaryfactory.com/ships/detail.asp?ship_id=Higgins-PT-Boat