The Guernsey Sea Cadets unit is struggling to find an alternative venue before its current home is replaced by a housing development.
The group is one of those affected by the closure of the former Boys' Grammar School, in Brock Road, later this year.
Its commanding officer Peter Derham said if they were unsuccessful it would be the end for the unit and its fleet of vessels.
He said: "Guernsey without a sea cadet unit would be absolutely unthinkable."
Mr Derham said: "We've been here for about 20 years, and the unit has been in the island for 26 years, the Education Council gave us this very old German-built wooden hut which has served the unit very well."
He said finding temporary, never mind permanent, accommodation for the group was proving difficult.
Mr Derham said while the offer of making use of some school sites had been discussed there were a lot of costs involved, which the charity would find it hard to generate.