Green’s Dictionary of Slang

1. (US Und.) a doughnut.

1916		Day Book (Chicago) 8 Sept. 17/1: ‘Couple of dougnuts and a cup of coffee without cream’ [...] ‘Two submarines and a mug of murk — no cow!’.
1922		[as cite 1916].
1931		Irwin Amer. Tramp and Und. Sl. 186: submarines.–Doughnuts.
1949		Monteleone Criminal Sl. (rev. edn).

2. (orig. milit.) a sausage roll.

1916

Yorks Eve. Post 16 Oct. 5/4: Munitions workers very glibly speak of sausages as ‘Zeppelins,’ and sausage rolls as ‘submarines,’ tea cakes as ‘doorsteps’ and a rock bun as ‘Hill 60’. Another [...] way of ordering a sausage roll is to ask for a ‘lucky-to-get-hold’.

3. (US, also sub) a type of large, over-filled sandwich; thus super-sub.

1949		N.Y. Herald Trib. 7 Aug. 24/2: Women with home freezers buy ‘subs’ in sets of a dozen to freeze, then defrost and serve when the crowd gathers.
1967		E. Liebow Tally’s Corner 20: Two shifts of two waitresses [...] fixing hamburgers, french fries, hot dogs, ‘half-smokes’ and ‘submarines’.
1987		T. Wolfe Bonfire of the Vanities 390: Ray was once more lunging across his desk eating a super-sub and drinking his vat of yellow coffee.
1989		(con. 1960) P. Theroux My Secret Hist. (1990) 107: ‘What can I do you for?’ ‘A large meatball sub.’.
1992		M. Leyner Et Tu, Babe (1993) 69: Maybe Lincoln had simply split a sopressata and smoked mozzarella sub with hot peppers and extra onions with Mary Todd.
2003		Guardian G2 29 Jan. 7: Never embarrass yourself again by asking for a hoagie in Vermont or a grinder in Philadelphia, when what you really want is what they call a hero in Maine or a poor boy in Louisiana (and a sub, pretty much everywhere else).
2013		K. Shea ‘Having Chiqui’ in ThugLit July-Aug. [ebook] Mike ‘Muzz’ Mukowski stopped eating his submarine sandwich [ibid.] Muzz [...] resumed sinking his teeth into the flank of the sub sandwich.

4. (US campus) a tampon.

1989

P. Munro Sl. U.

5. (N.Z. prison) a package of contraband hidden in a body cavity, thus v. to hide and carry such a package.

2001

D. Looser Boobslang [U. Canterbury D.Phil. thesis] 180/2: submarine n. a small package of contraband smuggled in the rectum or vagina [...] submarine v. to insert contraband into the rectum or vagina to smuggle it into, or out of, prison.