Babcock International's Annual Report in 2011 says it is "The largest supplier of support services to the Ministry of Defence."
Babcock International describes its involvement in producing the Royal Navy's new aircraft carrier's as “delivering a significant element of the Royal Navy's two new 65,000 tonne aircraft carriers”. These have been extremely controversial as one will be mothballed as soon as it is launched, and the chair of the Public Accounts Committee has estimated that costs for the carriers will rise to £12 billion.
Babcock International also works on current UK nuclear submarines. This includes the Astute class hunter-killer submarines, as well as the Vanguard class, which carry nuclear weapons.
The 2011 Annual Report states:"We already have a role in the development of the new deterrent submarines but we believe the strength of our expertise in submarine support and our ownership of unique naval nuclear infrastructure will provide opportunities for enhancing our long-term role in this programme."
They also have military contracts with other countries including Australia, New Zealand and Canada.
http://www.babcockinternational.com/about-us/library/annual-and-interim-results/ Babcock Annual Reports