The crew of the PT 73 moves from the Pacific to the Italian theatre of WWII when they are assigned to garrison duty in the Italian town of Voltafiore.
Trapped behind enemy lines, McHale, Parker, Gruber, and Tinker must pose as an Italian family in order to save themselves along with Binghamton and Carpenter.
Governor general Binghamton forbids fratenization between Naval personnel and the Voltafiore locals which doesn't go down well with either but soon finds he must make amends with the pending arrival of a VIP.
When McHale goes AWOL to try and spring Christy from the brig, his lookalike Italian cousin is recruited to replace him. Only one problem--the cousin speaks no English.
Trying to make money in the German souvenir racket, Gruber ends up getting himself, McHale, Harrigan, and the other crew members captured by the Germans. It's up to Parker and Fuji to save the day.
After Binghamton unfairly tosses Parker into the brig, McHale and Mayor Lugato conspire to get the Ensign released by preying on Binghamton's glory hungry nature.
Parker must pose as an Italian Contessa in order to keep the crew plus Binghamton and Harrigan out of trouble with a General.
With the General cracking down on wartime profiteering larcenous Mayor Lugato manages to trick McHale into going into the fishing business with him but it ends up working out better for the crew of the PT 73.
After moving into new quarters in an old wine cellar, the crew of the 73 has their furniture impounded by conniving Colonel Harrigan. McHale then devises a scheme to get the furniture back.
When rare wine is stolen by the Germans, Binghamton wants to retrieve it to give to the General as a gift, Mayor Lugato wants it for its cash value, and McHale and crew want to return it to its rightful owners.
McHale and Mayor Lugato are forced to team up in order to get the PT 73 crew out of the brig and the Voltafiore opera house re-opened.
Binghamton throws Mayor Lugato into the brig pending impeachment proceedings for running a racket in regard's to the town's fountain. To obtain the Mayor's release, the crew of the PT 73 must convince their captain that the fountain is jinxed.
After Harrigan commandeers McHale's beach quarters and forces them to move into town, the crew and Binghamton draw up conflcting plans to force the Army man out.
Binghamton finally has evidence to court martial McHale and crew so they must execute a complicated plan to locate its whereabouts before the JAG arrives on the scene. The plan involves making Binghamton think the war is over and it's 1950.
McHale's lookalike Italian cousin, Guiseppe, returns just in time to clear the 73 skipper of a desertion charge.
Ensign Parker tries unsuccessfully to steer three young Italian delinquents on the straight and narrow but when the PT 73 crew gets blamed for their misdeeds they end up trying to make things right.
Gruber and the guys use an old fire engine for their bootleg liquor deliveries but the scheme might come a cropper when Binghamton confiscates the vehicle for a town volunteer fire department he plans to launch.
Ensign Parker becomes a fugitive after an accident with a machine gun leaves him thinking that he's killed Binghamton.
McHale and the 73 crew try to help an AWOL WAC re-unite with her boyfriend before he ships out but Binghamton thinks she might be a German spy.
Binghamton's plan to get McHale in trouble with a visiting Congresswoman backfire and he's forced to team up with his nemesis to get his own neck out of the noose.
Binghamton is forced to rely on McHale and the 73 crew for help when he loses $1,000 to an Italian con man. The money had earlier been earmarked for the building of a golf course.
After a mischevious monkey steals an important document, it causes Binghamton to believe that McHale and Parker are enemy agents.
The crew of the Pt 73 persuades a female Ensign to provide them with contestants for a beauty contest and she ends up helping them capture a German U-boat too.
Binghamton sends McHale away for training and promotes Parker to the position of temporary skipper of the PT 73. He will have the position permanently if he can prove he's tough enough for the job. This newly gung ho Parker causes the rest of the crew to put in for transfers which was Binghamton's plan in the first place.
While Voltafiore is celebrating its 500th anniversary, Binghamton connives with a visiting Navy psychiatrist to have the crew of the PT 73 declared unfit for duty due to battle fatigue.
Binghamton and Parker are taken prisoner by a German patrol that has disguised themselves as American sailors.
When Parker accidentally wrecks Binghamton's Jeep he needs a replacement engine badly but the only one available is being used by a local racing driver for the upcoming Voltafiore Grand Prix race.
In violation of Binghamton's no fraternization order, the crew believes that Parker is keeping time with a beautiful Italian female named Angelina. Angelina is in reality a dog but when Parker let's slip that she's in a family way the you know what hits the fan.
When an Italian Count feels dishonored by Parker, he challenges him to a duel. Binghamton sees this as an opportunity to get rid of both Parker and McHale but then he dishonors the Count too.
Binghamton tries to ingratiate himself with a visiting political boss in order to embark upon a post-war Congressional career.