After the first batch was delivered the next three batches were the Leopard 1A1 model, which included a new gun stabilization system from Cadillac-Gage, allowing the tank to fire effectively on the move. The 1A1 also added the now-famous "skirts" along the sides to protect the upper tracks, and a new thermal jacket on the gun barrel to control heating. A less important change was to use rectangular rubber blocks fastened to the treads with a single pin instead of the earlier two-pin "shaped" versions.