Exactly when rock ‘n’ roll started is certainly open to debate but there is little doubt that its roots are found in swing, bop, blues, black and white gospel, hillbilly and old folksongs primarily from the Appalachian region and the South. But the kernel of rock ‘n’ roll was what is called “jump blues.” During World War II, there were many shortages—gasoline, rubber, metal, electricity, etc. Most venues for working bands either shut down or closed early to conserve electricity. Touring buses were scarce due to excessive consumption of gasoline and wear on tires which were difficult to replace due to the rubber shortage. So the big bands broke down into smaller touring units—trios, quartets, quintets, etc. They traveled around in cars which were far more economical and feasible.
The big band arrangements had to be stripped down and each instrument had a lot more space to work in. Bop jazz also helped with this transition being that it had also stripped down the jazz ensemble and often played quite wildly to fill musical space. But bop wasn’t a great dance music and these stripped down ensemble players wanted to play in the ballrooms for the dance crowd because that’s where the money was. So they played a form of jazzed up urbanized blues with a stiff dose of boogie-woogie for a jumpy melody and rhythm and hence the term jump blues.
Perhaps the forerunner of jump blues was the Goodman-Hampton piece “Flying Home” which was first performed in the 30s featuring Charlie Christian on that new-fangled electric guitar thing but by the 40s, all the small and large jazz combos were playing it and this is what gave birth to the genre of jump:
Flying Home - Illinois Jacquet - YouTube
Illinois Jacquet’s version of “Flying Home” (with Lionel Hampton) whose sax solo was said to be the start of jump and R&B.
The primary dance of jump blues was the jitterbug showing that jump was descended in part from swing:
Daisy Richardson - 1940's Jitterbug Dancer - YouTube
World War II was forcing all sorts of change in the American music landscape, the Japanese seized control of Southeast Asia and cut off all shipments of goods from that region that normally headed to the West. Among these goods was shellac. Shellac is made from a beetle called, appropriately enough, a lac beetle. These are extremely plentiful during mating season when millions of lac beetles cover every tree in the rain forests of Southeast Asia. Workers collect the beetles and boil them in large kettles which causes the beetles to exude a filmy substance from their bodies. This substance is scooped up from the surface of the boiling water where it floats, washed and processed to make shellac. Shellac was important in the West because that was what recording discs were made of. The shellac shortage caused the government to horde what stores of shellac it had access to which made commercial recordings hard to get.
The lac beetle.
Also in 1942, the American Federation of Musicians (AFM) centered in Chicago called a strike. The issue was over how musicians should be paid when recorded music was broadcast over the airwaves rather than live music. In days past, all broadcast music was live and so musician pay was not in dispute—if they played on the session, you paid them for it. But what about when a recording is played that a certain musician is on—should he get paid? The AFM said yes, the broadcasters said no. AFM president James C. Petrillo in Chicago called a strike while the question went before the courts. No AFM musicians could release recordings until then. Not until November of 1944 would the strike be called off. This sidelined most big name musicians from T-Bone Walker to Les Paul during the war. The exception to recording new music was V-discs which were made for American troops serving overseas. The court, by the way, ruled that musicians on broadcast recordings would not get paid for the broadcasts.