[1] On 13 August 1941, she was transferred to Motor Torpedo Boat Squadron One (MTBRON 1) under the command of Lt. William C. Specht and assigned to Pearl Harbor.

[1][2] During the attack on Pearl Harbor, PT-20 was moored at berth S-13 awaiting loading on the replenishment oiler USS Ramapo (AO-12) for MTBRON 1's assignment to the Philippines.

[3] All 12 boats of the squadron fired on the attacking Japanese aircraft with one, PT-23, credited with shooting down two Nakajima B5N "Kate" torpedo bombers.

[3] In May 1942, the squadron was reassigned to Lt. Clinton McKellar Jr. and tasked with the defense of Midway Island[3][4] being led by Marine Corps Colonel Harold D. Shannon.

[5] 11 of the 12 PT boats of MTBRON 1 made it to Midway (PT-23 had broken a crankshaft en route and was forced to return to Pearl Harbor).