When did Lionel drop the box latch coupler in favor of the knuckle coupler? Was the knuckle couple a purely post war phenomenon?
Thanks,
George
Yes. The knuckle coupler was developed during the war, and implemented in the first postwar production. Most early postwar engines and rolling stock were carryovers from the prewar line–so you will see very prewar-looking stamped steel cars bearing postwar knuckle couplers. And, of course, a number of people refitted their prewar pieces with postwar trucks, so you will sometimes also see actual prewar equipment riding on postwar trucks, too.
Anyone interested in the history of the (prototype) automatic coupler should look up the stories of Eli Janney, who invented it, and Lorenzo Coffin, who got the railroads to use it.