JATO stands for Jet Assisted Take Off. If that seems odd, since the concept utilized a rocket rather than a jet engine, it is also known as RATO. The first JATO takeoff in the U.S. appears to have been accomplished with a 174-lb thrust black powder rocket under an XPQ-13, which was an ERCO Ercoupe acquired by the Army. The test was accomplished at March Field in California.
A 50% reduction in takeoff distance was demonstrated, with the rocket burning for 12 seconds.
Both the Army and the Navy recognized the benefit that JATO could provide for a takeoff assist from short fields or for an overloaded airplane. The Navy was particularly interested in using JATO for carrier takeoffs in place of the catapult and for safer takeoffs of seaplanes from a restricted harbor or rough seas. A series of demonstrations were conducted with various carrier-based airplanes and seaplanes.
The bottles were generally mounted on three hooks, one to transfer the thrust of the JATO to the airplane and two to stabilize the bottle.
It had also been essential for the takeoff of the P2V "The Turtle" on its record-braking long distance flight in 1946: http://thanlont.blogspot.com/2016/09/the-turtles-takeoff.html
The original JATO bottles created a great deal of smoke. Improvements resulted in a standardized 1,000-lb thrust unit of 15 seconds duration that was relatively smokeless.
One post-World War II carrier application was for deck launching an AD Skyraider armed with a Mk 7 nuclear weapon.
The Douglas A3D Skywarrior was provided with a major JATO assist, presumably for a deck-run takeoff if the catapults were out of service:
One oddity of the A3D installation was that the usual arrangement of one thrust hook forward and two stabilizing hooks aft was reversed.
Note that the A3D and B-66 JATO provisions were permanent. The A4D could also be fitted with JATO for deck-run and short-field takeoffs, but this required the installation of dive brakes with JATO mounting capability.
One 4,500-lb unit could be mounted on each speed brake.
One interesting aspect of a JATO-assisted takeoff is that the shortest takeoff distance, given the limited time of thrust, was achieved when the JATOs were fired so that they burned out just as highest obstacle for a non-JATO climb angle is cleared. This meant that they had to be fired at some predetermined point during the takeoff roll.