Sikorsky—H-53 Pave Low: USAF Variants and Serials CH-53A: Two surplus US Marine Corps CH-53As were transferred to the Air Force, adopting period serial allocations. · 63-13693 to 63-13694 HH-53B: Long-range search and rescue version of the USMC CH-53A with an air refueling probe and external rescue hoist. · 66-14428 to 66-14435 TH-53A: Six USMC CH-53As were redesignated to TH-53A standard for training duties with MAC. · 66-14468 to 66-14473 CH-53C: Cargo/assault version of the HH-53C. · 68-10922 to 68-10933; 70-1625 to 70-1632 HH-53C: Similar to the HH-53B but with an uprated engine and other minor improvements. · 67-14993 to 67-14996; 68-8283 to 68-8286; 68-10354 to 68-10369; 69-5784 to 69-5797; 73-1647 to 73-1652 Conversion designations NCH-53A: One of the CH-53As was assigned to permanent test duties connected with the launch and recovery of unmanned drones. · 63-13694 MH-53H: A small number of CH/HH-53Cs were modified with nose-mounted FLIR, terrain-following radar and improved navigation equipment for special operations and combat rescue duties. · 68-10923; 69-5791; 73-1647; 73-1648; 73-1649; 73-1650; 73-1651; plus others modified to MH-53J configuration MH-53J: Advanced version of the MH-53H with terrain-following/avoidance radar, advanced avionics and ECM, secure communications, and global positioning system terminals. · 66-14428; 66-14429; 66-14431 to 66-14433; 67-14993 to 67-14995; 68-8284; 68-8286; 68-10356 to 68-10358; 68-10360; 68-10363; 68-10364; 68-10367; 68-10369; 68-10923; 68-10924; 68-10928; 68-10930; 68-10932; 69-5784; 69-5785; 69-5789 to 69-5791; 69-5793 to 69-5797; 70-1629 to 70-1631; 73-1649; 73-1652 plus others