The Mark XX mounting permitted an increased elevation to 50 degrees (compared to 40 for previous marks). However, this still limited the engagement time against enemy aircraft, although medium calibre guns posed little threat to dive bombers prior to the use of radar proximity fuzed ammunition. The Imperial Japanese Navy had already introduced a 5-inch (127 mm) gun with 70-degree elevation into service which had very poor performance as an anti-aircraft weapon, while the United States Navy's 5"/38 cal Mark 32 mount could elevate to 85 degrees. The 4.5-inch (114 mm) guns fitted to "Ark Royal" were already in service and capable of elevations of 80 degrees, although the mountings were not suitable for a destroyer-size ship. Coupled with the lack of powered elevation, the Mark XX mounting was compromised in its chosen anti-aircraft role, although it compared favourably with any similar weapon in the Axis inventory.