The initial training to be a special forces operator is 3.5 years, the longest anywhere but the training is also a continuous process, in the special forces, the members are imparted both basic and advance training. They are taught specialised mode of infiltration and exfiltration, either by air (combat freefall) or sea (combat diving). Some trainees return to PTS to undergo the free-fall course, which requires at least 50 jumps from altitudes up to 33,500 feet to pass. Both HALO (High Altitude Low Opening) and HAHO (High Altitude High Opening) techniques are learned. The ability to use the HAHO method and specially designed maneuverable parachutes called HAPPS (High Altitude Parachute Penetration System)/AMX-310 to conduct stealth insertions over distances up to 50 km is also perfected.