The plaintiff below claimed exemption from militia duty because he commanded a sloop which sailed on the Hudson river, between Poughkeepsie and New-York. The exemption in the act of congress, (Laws U. States, vol. 2. 93.) applicable to the case, is, “ of all mariners actually employed in the sea service of any citizen or merchant within the United States.” The plaintiff was certainly not a mariner within the purview of this act, for he had nothing to do with the sea service. M he act of this state (33d sess. c. 121. s. 24.) adopts this construction ; for it admits expressly, that “ persons employed in tíie coasting trade” are not to be exempted from duty, and the consequent penalty for omission to perform it. This point is sufficient to reverse the judgment, and the court, therefore, forbear to give an opinion, whether the decision of a court martial, on a question of which they have due cognisance, can ever be reviewed or traversed in a collateral action. The judgment below must be reversed.