David,

Fort Myer, Virginia is named after the US Army's first signal officer, Albert James Myer. Prior to his accepting the SO's position as a major with lateral pay-grade statis parrallel to that of a cavalry officer, Myer had been an assistant surgeon for the army with the rank of Lieut.

A quick review of the US Army Revised Regulations of 1861 might shed light as to what an assistant-surgeon's pay-grade would have been equal to amongst the other ranks.

Much Success,
Walt Mathers
(An ordinary signal flag-flopper) ~~~~~~~~~~~~~~~~~~~~~~~