[1] The Mk.5 seat was developed alongside the Mk.4 design to meet the needs of the United States Navy.

Compared to the Mk.4 seat the structure and harnesses were strengthened to withstand higher crash landing loads, this resulted in a slight increase in weight.

[2] Two aircraft types operated by the Royal Norwegian Air Force, the RF-84F Thunderflash and the F-86D Sabre, were retro-fitted with Mk.5 seats at the Martin-Baker company's home airfield at Chalgrove.

As the seat moves up its guide rails an emergency oxygen supply is activated and personal equipment tubing and communication leads are automatically disconnected, leg restraints also operate.

[2] A steel rod, known as the drogue gun, is fired and extracts two small parachutes to stabilise the seat's descent path.