Each engine had an impulse starter, a black powder starting cartridge, that allowed the B-57 to start its engines without the use of an APU cart. The problem was the huge amounts of thick smoke generated made it appear the engines were on fire. Crews soon learned to start engines with the canopy closed, even in SEA lest some over zealous crash crew try to put out the fire with foam (with them in the cockpit).
The B-57, like the F-105 Thunderchief, had a rotary bomb bay door. Ordnance was attached to the door itself. In flight, the door would rotate and the bombs were pickled off the bomb bay door. The rotary bomb door eliminated the drag caused buy conventional doors when it came to weapons release. On the F-105, the rotary bomb bay door option was rarely used and the bay was taken up by a long range fuel tank for raids over North Viet Nam.
Between visiting B-57s and our own K-135s both doing cart starts big black clouds of smoke that could be seen for miles were common at Plattsburgh. The FB-111s had the capability for a cart start but they rarely used it. Sometimes the heavy black smoke formed into mushroom clouds, not exactly what anyone wants to see at a nuke bomber base.