A Threat To The Republic

[L Verge]

Which unit was in charge of guarding the bridge? Sgt. Cobb was with the 3rd Massachusetts Heavy Artillery throughout his service (most of which was in D.C. to fortify the city, where he was based out of Fort Baker), but I think that the other sentries with him that night were with the 10th Regiment of the Veterans Reserve Corps. Which army records are missing?