Dictionary coverage of 'get cracking'
J.E. Lighter, Random House Historical Dictionary of American Slang (1994) reports that "get cracking" came into U.S. English from the UK during the 1940s:
get cracking to get busy; get going. {This phr[ase] came into U.S. speech through contact with British armed forces during WWII.}
Lighter's first citation for the phrase is from Eric Partridge, Dictionary of Slang and Unconventional English (1936), as "Get cracking, begin work."
It appears to have caught on as a naturalized phrase fairly quickly, however, since it appears in Harold Wentworth & Stuart Flexner, Dictionary of American Slang, first edition (1960):
cracking, get Start; start moving; begin working; begin to exert oneself. Often in the phrase let's get cracking.
The entry for "get cracking" in the original edition of Eric Partridge, Dictionary of Slang and Unconventional English (1936) is actually a bit more detailed than Lighter's citation suggests:
get cracking. To begin work : Royal Air Force : from ca. 1925. I.e. cracking on speed.
Earlier in the same dictionary, Partridge has this entry for cracking as an adjective:
cracking, adj. Very fast ; exceedingly vigorous (-- 1880) : slightly ob[solete, in 1936]
By the fifth edition (1961) of the dictionary, however, Partridge had evidently rethought the place of "get cracking" in the larger scheme of similar phrases and had adopted the entry that ghoppe reports in a different answer here, with the suggestion that it might have its origin in "whip-cracking at the mustering of cattle."
Early Google Books matches
Google Search results generally support Partridge's1936 reading of the phrase. The earliest relevant matches are from 1938, and one of them is RAF-specific. From Popular Flying, volume 6, issue 9 (1938) [combined snippets]:
We've got a new vocabulary in Black Bourton, the vocabulary of the R.A.F. Nice things are "wizard"; nasty people are "ropey types," and a reckless man is "split." One is "browned off" when one is rather depressed; the ground is the "deck" and the sky is the "ceiling"; dull-witted people are "drips," and when in a hurry we ask each other to get "cracking." This strange lingo is, of course, subject to changes and ex-R.A.F. men of several years ago would find themselves hopelessly dated by the expressions they use.
There is, however, one outlying instance of "got cracking"—or more precisely "got cracking away"—that might be significant as well. From Bertram Milford, In the Whirl of the Rising (1904), a novel seemingly set in Rhodesia during the Second Matabele War, of 1896–1897:
"You must have had the very devil of a scrap, Peters." one of these [horsemen from Green's Scouts, a relieving force] was saying. "We could hear you banging away from the time you began, and pushed our gees for all they'd carry; for we reckoned all that shooting meant a big thing and no bally skirmish. ... They [the Matabele forces] didn't know we were there till we got cracking away right in their faces, or mostly backs. Magtig! Didn't they skip. ..."
Here it seems pretty clear that "got cracking away" means "started firing our guns." Is this usage connected to the later World War II use of "get cracking"? It's difficult to say. If there is a connection, the literal slang term for gunfire would have to have transmuted into a more figurative sense of getting started. Still, both usages have a strong tie to military usage, and a connection is not impossible.
Conclusion
No reference work has convincingly tracked "get cracking" to its original lair. The term does seem to be of UK English origin, but whether it originated in the RAF in 1925, or in Rhodesia in the late 1890s, or in some bucolic setting to the sound of bullwhips bring cattle into order for transportation or migration remains unclear.
I've only ever heard the pleased meaning.
The OED says chuffed is originally military slang, and has both meanings. The "pleased, satisfied" meaning has four quotations from 1957 to 1967, whilst the "displeased, disgruntled" meaning has two, in 1960 and 1964. One is from David Storey's This Sporting Life and the other is from Celia Dale's Other people.
Norman W. Schur's British English A to Zed (2001) says:
Slang. This curious bit of antiquated army slang has two diametrically opposite meanings, depending on the context. One can say chuffed pink (tickled pink) to mean 'pleased' or dead chuffed to mean 'displeased.' In the second sense,chuffed is synonymous with choked.
The New Partridge Dictionary of Slang and Unconventional English (2008) says:
chuffed adjective 1 pleased, delighted; flattered; very excited. Originally northern English dialect meaning ‘proud’, adopted by military, then wider society. The current, more generalised usage was possibly spread by jazz fans. Embellishments include ‘chuffed to fuck’; ‘chuffed to arseholes’; ‘chuffed to buggery’; ‘chuffed pink’; ‘chuffed to little mint-balls’; ‘bo-chuffed’; ‘chuffed to little naffy breaks’; ‘chuffed to naffy breaks’ and ‘chuffed to oil-bumps’. Often qualified by intensifiers DEAD, REAL, WELL, etc UK, 1957.
2 displeased, disgruntled. Qualifiers and context may be required to distinguish usage from the previous sense as ‘pleased’. Variants include ‘dischuffed’ and ‘dead chuffed’ UK, 1961
Best Answer
According to Wikipedia, both English versions derive from a Scottish expression "possession is eleven points in the law, and they say there are but twelve". Wikipedia itself doesn't have a source or etymology for that expression, but I found it in a play by Colley Cibber, "Woman's Wit", from the late 1600s, so it's at least that old.
The term's basic meaning is simply that the overwhelming majority of statutes in the law are based on, or define and regulate, possession of things of value, such as goods, services rendered, money and land. So, at its core it's simply a statement of a known truth.
However, the term as commonly used is a synonym for "finder's keepers", thus referring to a key point involving possession. The fact that a person is in possession of some item of value is usually prima facie that that person is the legal owner of said item, and absent any evidence of a superior claim to the item, or that the person in possession acquired it illegally, that decision will stand. In terms of things which are not legal to possess, the possession is prima facie that the owner is guilty of the crime, and will be found so if there is no compelling evidence to refute it.
The term is also often used to describe "adverse possession of real property". Simply stated, a person who finds apparently abandoned or unimproved land, improves said property and occupies it for a time without hindrance, is considered the "adverse owner" of that property and is entitled to it, despite there possibly being an "actual owner" who holds a title to the land. Adverse possession is also the legal concept behind liens; a person who has improved some property knowingly belonging to another has a claim on a portion of the property equal to the value of improvements rendered, until settled by some other means. There are similar statutes for material goods; if you find money or something else of value, and nobody else offers a valid claim to it given reasonable opportunity, it's yours.