SIR – In his headlong rush to replace Trident, Philip Hammond, the Defence Secretary, seems to be overlooking the basic question of whether it remains viable for Britain to continue independently developing and maintaining its own nuclear submarines (report, June 18). He should take into account the chronic squeeze on British defence funding, the limited number of hulls it can afford, ever more stringent safety standards, and the long-term erosion of Britain's nuclear expertise. By developing an independent design for the new submarine, the Government is opening itself up to allegations that the Trident replacement programme is just an excuse...