vests. A ribbed material lining on the inside of the Mk 4 vests improves breathability in hotter climates such as that of Afghanistan. Both Mk 4 vests have a higher number of MOLLE loops compared to earlier versions and introduced new pouches such as a "commander's pouch" for holding stationery and open magazine pouches with elastic draw-cords for easier access to ammunition (though conventional pouches with Velcro flaps and Fastex fastenings were also included). Osprey Mk 4 and Mk 4A body armour has mostly been replaced by the Scalable Tactical Vest component of Virtus body armour, which is even lighter and closer-fitting and can have its level of protection more closely scaled to the prevailing threat type. The vest also features a quick-release mechanism to aid safe extraction from hazardous situations such as burning vehicles or drowning and a dynamic weight distribution system which, when linked to a soldier's waist belt, aids in spreading the soldier's load across the back, shoulders, and hips; a mechanism in the small of the back allows the wearer to adjust the weight bias depending on the situation. Ancillary to regular body armour is a three-tier pelvic armour system issued since 2010 to mitigate against shrapnel and other blast effects. The first layer is a pair of underwear shorts manufactured from a ballistic silk material. The second layer consists of detachable pelvic body armour that is intended to be worn while 'outside the wire' to meet the greater threats faced by soldiers on patrol; it can be rolled up and clipped to a belt and then pulled through the legs to form a protective pouch, ensuring that mobility is not impeded while worn. The third layer consists of knee-length ballistic shorts worn over a soldier's combat trousers, offering coverage of the upper leg and wider abdominal region and designed for use by soldiers operating hand-held metal detectors to search for explosive devices or otherwise serving in a combat role where greater levels of protection are required. Respirator By January 2015, over 300,000 General Service Respirators had been delivered to replace the older S10 respirator. These respirators are also used by the Royal Navy, Royal Air Force and Royal Fleet Auxiliary. Uniforms Boots In 2012, the MOD purchased a newly designed range of brown combat boots from Haix, Alt-Berg, and other manufacturers for the Army, Royal Navy and RAF to replace the black and desert combat