In the wake of the shooting tragedies at Dunblane and in Tasmania, parents believe the decision of governors at the Thomas Hardye school, Dorchester, is particularly insensitive.
Trish Davis, who has a child at the school, said: "Many parents think it is inappropriate for a local comprehensive to have such a thing on its premises. The ethos in school would be effected." She added: "I think a CCF is an anachronism."
Nationally, 243 schools run a CCF and 43 of these are state schools. Nearly 38,000 young people are cadets, with 4,700 girl members.
Zofia Dymitr, whose daughter attends Thomas Hardye, said parents were concerned they had not been consulted on the issue. "Money should not be invested in building this armoury for so few people. In society we should be looking to limit the availability of firearms."
The 1,400-pupil comprehensive was created four years ago for 13 to 18-year-olds by the amalgamation of two schools. One of those had a CCF and an armoury on its site that has now been sold.
Governors are now considering building a replacement armoury and rifle range. The CCF's guns are currently under lock and key at an army camp.
Some governors are opposed to the project and their position has been strengthened by the parents' opposition.
The move to build the armoury was strongly backed by governors from military backgrounds, including a retired general and naval commander. Forty per cent of officers in the army were members of their school's CCF.
Jim Read, chairman of the charity trustees of the Thomas Hardye Foundation, said the project should be dropped on cost grounds alone. The bill for the new building is expected to be Pounds 35,000.
"Some of the governors aired their views about wanting an armoury back in the school, but the whole thing should be abandoned. What concerns me is the effect on teaching staff who are not directly involved, but may get some of the blame," he said. "In the present age in state schools the CCF doesn't have a place."
A Ministry of Defence spokesman, which helps fund the CCF, said the rifles that are kept in school armouries are for small-bore shooting and the ranges met police standards.
"One of the advantages of the CCF is that it can educate young people who want to do sport shooting in the responsible and safe use of firearms. Safety is paramount," he said. He added that the massacres at Dunblane primary school and in Tasmania were not not a sensitive issue for the CCF as they had involved the irresponsible use of firearms.