They were solid-fuel rockets
but I don't know the fuel. They were probably standard JATO units from the period. Back in the 1950s, planes like the B-47 often used JATO (jet assisted take-off) rockets because they were so underpowered and had a high takeoff speed. Without the JATOs, a fully loaded B-47 would need a runway 2-3 miles long to takeoff. JATOs are still sometimes used on C-130s. The Blue Angles C-130 "Fat Albert" often demonstrates a JATO takeoff at airshows. It appears today's JATO units burn a lot cleaner than the ones from the 1950s.
