The British Royal Navy has ordered 65 Tomahawk Block IV Torpedo Launched Land-Attack missiles. These are the primary (most frequently used) weapons of British SSNs, which use torpedo tubes to fire torpedoes or Tomahawks.
The new Astute class SSNs can carry 38 torpedoes or Tomahawks. Britain has one Astute in service and another six on the way. The previous seven Trafalgar class SSNs only carried 30 torpedoes or Tomahawks. Thus until recently the Royal Navy maintained an inventory of less than a hundred Tomahawks. Dozens were used during the 2011 operations against Libya so this order will replenish the inventory and expand it to accommodate the larger missile capability of the Astutes. Three of the Trafalgars have been retired and the new Astutes are entering service soon (one is being readied for service and four are under construction).
The RGM-109E Block IV Tomahawk Land Attack Missile weighs 1.2 ton, is six meters (18 feet) long, has a range of 1,600 kilometers, getting there at a speed of 600-900 kilometers an hour, flying at an altitude of 17-32 meters (50-100 feet), and propelled by a jet engine generating only 273 kg (600 pounds) of thrust. Accuracy is on a par with JDAM (10 meters/ 31 feet). The Block IV Tomahawk can be reprogrammed in flight to hit another target and carries a vidcam to allow someone to check on prospective targets. There’s also the new JMEW (Joint Multi-Effects Warhead System) warhead for the Tomahawk. This is a 450 kg (1,000 pound) warhead designed mainly for penetrating underground bunkers, but it will also provide excellent blast effect for less robust targets. Exact penetration was not revealed. JMEW uses laser terminal guidance, enabling it to hit within a few meters (ten feet) of its aiming point. JMEW can also hit moving targets. Most Tomahawks in U.S. service are fired from surface ships while Britain only uses them from subs.