Sons of the Sea is the fourteenth and final episode of the third series of the British comedy series Dad's Army that was originally transmitted on 11 December 1969.
When the bank inherits a boat, the platoon is able to mount a river patrol - and ends up lost in the English Channel.
Mr Maxwell, the solicitor for the late Mr Johnson, tells Mainwaring and Wilson that the only things he left of any value are the clothes he stood up in, and his boat The Naughty Jane. Wilson adds that Mr Johnson's account was overdrawn to the extent of £33 12s 6d. Mainwaring admits that that means the boat becomes the property of the bank, and can be used to offset the overdraft.
Just as Mr Maxwell leaves, Mainwaring has an idea, much to Wilson's panic: the platoon can use that boat for river patrols and tells him that half a dozen determined men, armed to the teeth, can play havoc with the Nazis if they invaded. Wilson tells Mainwaring that the platoon work hard enough as it is, and deserve a rest. Mainwaring tells Wilson that he only wants to test it out and decides to call for volunteers. He chooses Jones, Pike, Walker, Desmond, Godfrey and Frazer.
They hold a practice in the church hall using chairs and mops. Mainwaring's lack of nautical knowledge annoys Frazer, who holds the most claim to being an experienced sailor. It isn't long before they get it out on the open water. Mainwaring says they'll just row up to the mouth of the river and turn back. However, it soon turns foggy, and Mainwaring decides to turn round. It isn't long before Mainwaring takes charge completely, and Frazer goes into a sulk.
Night falls, and Mainwaring says they must be well up-stream by now. Pike is ill, and wants a drink; Walker scoops some water with his forage cap and gives it to Pike, who promptly spits it out because it's salty. They're in the middle of the English Channel. Frazer refuses to help, still stung after being spurned by Mainwaring, so the men have to come up with their own ideas, with little success. Mainwaring is proud of the men's loyalty, and Frazer, realising his stupidity, apologises to Mainwaring, and he accepts his apology. Mainwaring asks him where the North is, but Frazer doesn't know either.
As dawn breaks, Jones hears voices from the shore. Elated, they row into the shore, and prepare to call out, but are interrupted by French singing (in actual fact, French Canadian pilots celebrating a successful mission in a nearby pub). Mainwaring believes that they must have drifted into France. They sneak into an empty railway truck, and make themselves comfortable, so they can escape the next night.
Jones is woken by the sound of wheels turning, and is shocked when he opens the truck door and sees the train moving. He alerts Mainwaring, who in turn wakens the platoon, and they prepare to jump off, stop by stop, and make their way back to the coast to get back to England. They throw their rifle bolts and the Lewis Gun's butterfly spring out of the door, and stuff their hats and jackets up their tunics. As the train stops, they open the door, and spot a man on the station. Using schoolboy French, they attempt to bluff their way out of it. However, it turns out they're at Eastbourne Station. They prepare to head back to Walmington-on-Sea by train for lunch, but Mainwaring bursts their bubble by reminding them they have to pick up the rifle bolts and they set off back down the tracks.