Green’s Dictionary of Slang

1. (also red one) the penis.

1904		Lustful Memoirs of a Young and Passionated Girl 38–9: He laid across the bed on his back, his charmer hard and stiff like a column of ivory with a red cap on it.
1966		Trimble 5000 Adult Sex Words and Phrases.
1973		(con. 1940s–60s) Hogbotel & ffuckes ‘Cats on the Rooftops’ in Snatches and Lays 25: The labors of the poofter find but little favor here, / But the morally leprous bastard has a peaceful sleep, I fear, / As he dreams he rips a red ’un up some dirty urchin’s rear.

2. (orig. milit., also cherry-nob) a military police officer.

1916		C.J. Dennis ‘The Battle of the Wazzir’ in Moods of Ginger Mick [unpub. unrev. proof version] n.p.: Then the Redcaps come to argue, but they jist amused the mob.
1916		‘Anzac’ On the Anzac Trail 102: Another interruption! This time from the ‘Red Caps,’ the military police.
1918		Aussie (France) VIII Oct. 14/1: Then look at those pongos who dolled themselves up as W.A.A.C’s and tooted down to Paris. [...] Of course, there was a bust-up all round, and the roar of the mix-up that naturally followed brought up a whole platoon of Red-caps.
1919		Athenaeum 1 Aug. 695/1: In your July 18 issue a correspondent mentions ‘red-hat’ as an army policeman. I have always found ‘red-cap’ to be the more familiar term [OED].
1921		N&Q 12 Ser. IX 344: Red Caps. Military Police. [Ibid.] 383: Cherry-Nobs. Military police.
1930		(con. 1914–18) Brophy & Partridge Songs and Sl. of the British Soldier.
1945		J. Maclaren-Ross Swag, the Spy and the Soldier in Lehmann Penguin New Writing No. 26 54: Sandy had been picked up by red-caps.
1956		‘Charles Raven’ Und. Nights 150: He gave them so much trouble, smashing up everything and everybody in reach and refusing to let the redcaps get him down.
1965		(con. 1940s) B. Behan Confessions 78: I did not think it was possible to hurt the feelings of a Redcap (as we commonly called a military policeman).
1971		(con. WWII) B. Aldiss Soldier Erect 169: Suppose the Redcaps pick us up? What if someone caught us doing it?
1988		J. Healy Grass Arena (1990) 31: The Redcaps brought you in.
2012		(con. 1943) G.S. Manson Irish Fandango [ebook] ‘I’ll dob ya in to the redcaps and you’ll go into a military prison’.

3. (US) a railway porter; an airline porter, thus v. to work as a porter.

1910		Omaha Dly Bee (NE) 9 Sept. 11/6: [caption] Redcap at Union Station Shows His Qualifications.
1919		F. Hurst ‘The Wrong Pew’ in Humoresque 331: A redcap, wild for fee, swung open the cab door.
1920		R. Lardner Big Town 95: A redcap helped load us on over to the station.
1936		A.E. Duckett ‘Truckin ’round Brooklyn’ in N.Y. Age 25 July 7/1: Archie Miller is red-capping.
1937		J.M. Cain Serenade (1985) 275: I gave my bag to a redcap.
1947		F. Brown Fabulous Clipjoint (1949) 169: The redcap was picking up the bags.
1958		R. Chandler Playback 15: He [...] went with the redcap to a locker.
1968		K. Brasselle Cannibals 380: We are now at my airline departure building. I got out, gave my two-suiter to the redcap.
1977		S. Kernochan Dry Hustle 192: If the redcap or somebody asks for our baggage tickets, you point me out over there.

4. (drugs) in pl., generic for crack cocaine [the red-capped vial in which the drug is often sold].

1989		(con. 1982–6) T. Williams Cocaine Kids (1990) 133: On the corner of 162nd Street, three boys and two girls shout to me [...] ‘got that coke, got that crack, got red caps, got blues, got yellow ones – you choose. What you want, my friend? What you need?’.
1992		N. George ‘Cool vs. Chilly’ in Buppies, B-Boys, Baps and Bohos (1994) 69: Before the sale of trey bags gave way to red caps.
2001		ONDCP Street Terms 18: Red caps — Crack Cocaine.