Following lessons identified in Iraq by both British and US forces, including the death of Sergeant Steven Roberts, the Osprey armour system was released in 2006 for general use.

In response to lessons learned in combat, the British Army developed the Virtus personal armour system that offers the same protection as Osprey, but is significantly lighter, moves with the body more easily, and produces a slimmer profile.

The level of protection can be increased or decreased depending on the threat environment by adding or removing soft armour pads and hard ballistic plates.

Unlike the Osprey's Velcro straps, the Virtus has a chest-positioned pin quick-release mechanism that releases the entire body kit when pulled for safe extraction in hazardous situations.

A new, lighter helmet provides increased blunt impact protection, face and mandible guards for certain roles, and a shape designed to work with the armour and daysack so weapons can be comfortably used even in a prone position; it has a permanent universal mount for night vision gear and a scalable counterweight attached to the rear to ease strain on the wearer's neck.

[13] Optional collar attachments (available in half and full versions) and arm protectors (consisting of brassards and shoulder guards), each with their own soft armour fillers, provide further protection; an Osprey vest thus configured is referred to as 'Complete Fighting Order', but normally the vest is worn in 'Light Fighting Order' without the addition of collar and arm protection.

The pouch system consists of a range of accessories that can be fitted to the vest, allowing an easily configurable load carrying capability that can be tailored to the needs of the individual user.

Soldiers were discouraged from carrying items such as bayonets, pens, or cyalume torches on the front of the Osprey vest in order to prevent facial injury in the event of a blast.

Finally, the most striking change when compared to previous iterations is that the front and rear hard armour plates are now carried internally rather than in an external pocket; combined with the plates being made thinner without reducing effectiveness, this means that the Mk 4 vest provides the same ballistic protection as earlier Osprey vests while being more comfortable to wear, closer fitting, and easier to move in.

Initial criticisms of the first generation were related to the significant increase in weight, and size of the ballistic plates, compared with the existing ECBA.