The Royal Navy's 1936 Naval Programme authorised the construction of two aircraft carriers. Admiral Sir Reginald Henderson, Third Sea Lord and Controller of the Navy, was determined not to simply modify the previous unarmoured design. He believed that carriers could not be successfully defended by their own aircraft without some form of early-warning system. Lacking that, there was nothing to prevent land-based aircraft from attacking them, especially in confined waters like the North Sea and Mediterranean. This meant that the ship had to be capable of remaining in action after sustaining damage and that her fragile aircraft had to be protected entirely from damage. The only way to do this was to completely armour the hangar in which the aircraft would shelter, but putting so much weight high in the ship allowed only a single-storey hangar due to stability concerns. This halved the aircraft capacity compared with the older unarmoured carriers, exchanging offensive potential for defensive survivability.