In December 1941, Lieutenant John "Brick" Brickley (Robert Montgomery) commands a squadron of small yet nimble U.S. Navy PT boats stationed at Cavite in the Philippines. As he attempts to demonstrate their remarkable agility and seakeeping abilities to Admiral Blackwell (Charles Trowbridge), the senior commander remains unenthusiastic, brushing off their small size and light construction. This dismissal leaves Lieutenant Junior Grade "Rusty" Ryan (John Wayne) increasingly frustrated, as his urge to engage in combat intensifies. When the news of the Japanese assault on Pearl Harbor breaks through a radio bulletin, Rusty's agitation only escalates, highlighting his fervent aspiration to join the fight.
As Japanese forces wreak havoc across the Philippines, Brick's squadron finds itself sidelined, assigned mundane tasks like mail and messenger duties. The growing tension between Brick and Rusty teeters on the edge of explosion, especially after a brutal attack on their base prompts the admiral to command them to attack a formidable Japanese cruiser bombarding U.S. troop positions onshore.
Initially, Brick designates Rusty to lead the second boat in the mission; however, discovering his executive officer suffers from blood poisoning from a prior battle wound, he reassesses and sends Rusty to sick bay, choosing a different crew to replace him. Bitter and resentful, Rusty accuses his commanding officer of "glory hogging," resisting evacuation to a military hospital on Corregidor. Eventually, after acknowledging the seriousness of his condition, he meets Ohio (Louis Jean Heydt), who encourages him to calm down and accept his fate.
During Rusty's recovery, he blossoms into a romance with the determined Army nurse Sandy Davyss (Donna Reed), whose wholesome personality manages to impress even Ohio, another patient sharing the quarters. While Brick triumphantly sinks the Japanese cruiser, Rusty returns to the squadron, which then celebrates a string of victories, although at a mounting cost of boats and crew.
However, the dire conditions foreshadow the inevitable fall of the Philippines. As the situation worsens, Sandy participates in a dinner honoring her, rekindling the affection between her and Rusty. As Japanese forces relentlessly move through the Philippines, the PT Squadron finds themselves trapped on Corregidor, the last stronghold in Manila Bay after the American defenses at Bataan have crumbled. Under the orders of General Douglas MacArthur (Douglas MacArthur), Rusty and his comrades are tasked with evacuating the commanding general, alongside Admiral Blackwell and their entourage, to Mindanao, for transport to Australia. In a heart-wrenching moment, Rusty makes a final phone call to Sandy, who is stationed in Bataan, only for the line to be cut abruptly before their goodbye.
Navigating perilous waters, the PT flotilla successfully transports the leaders to safety but continues to harass the Japanese forces despite their numbers diminishing alarmingly. With the squadron's strength waning, those without boats are repurposed to fight as infantry alongside the Army. Rusty's own vessel takes a hit, leading him to seek repairs at a small shipyard managed by the seasoned "Dad" Knowland (Russell Simpson). As his boat is prepped for departure ahead of an impending Japanese onslaught, Dad refuses to evacuate, bidding a poignant farewell to Rusty and the team as they abandon their damaged craft.
In those crucial last hours of warfare, Rusty's boat bravely launches one last daring assault against an intimidating cruiser, sacrificing itself in the process. With Brick's vessel commandeered by the Army for messenger duties, the remaining PT boats have been reduced, shrouded in remnants of their past glory. Rusty, Brick, and two ensigns receive orders from Navy command to be airlifted to safety and assigned to training roles stateside to prepare new PT crews for future battles. While they await their flight, Rusty encounters Ohio, both unaware of Sandy's fate as she remains trapped behind enemy lines in Bataan. Sharing their fears and uncertainties, they provide comfort in one another's presence, clinging to hope for Sandy's safe escape.
As the ensigns arrive late, Rusty makes a desperate attempt to secure his place on the flight, only to be reminded of his duty by Brickley. Ohio reluctantly gives up his seat, left behind to face a likely capture or death at the hands of their merciless adversaries. Meanwhile, as the last of the American forces, led by the steadfast Chief Mulcahey (Ward Bond), take up arms again, they join the tattered remnants of the U.S. Army and the brave Filipino guerrillas, embarking on a perilous crusade to reignite the faltering resistance. Much like the PT boats that once represented the pinnacle of American valor, these soldiers now find themselves expendable in the struggle, their very survival hinging precariously on the outcome of a seemingly futile battle against their formidable foes.
