volunteer navy

from the GNU version of the Collaborative International Dictionary of English.

• A navy of vessels fitted out and manned by volunteers who sail under the flag of the regular navy and subject to naval discipline. Prussia in 1870, in the Franco-German war, organized such a navy, which was commanded by merchant seamen with temporary commissions, with the claim (in which England acquiesced) that it did not come within the meaning of the term privateer.