Major General Benjamin F. Butler

It was difficult to supply troops on the move with postage stamps (especially troops who were not paid regularly!), so the US government early in the war instituted a policy whereby troops could send letters collect. (These were NOT 'free postage paid by recipient' -- they were collect, postage paid by recipient. The distinction is perhaps subtle but important, as there are a remarkable number of free-franked soldier's covers, and several very rare instances free soldier's mail).

Soldiers could prepay postage when stamps were available. This is seen most frequently: 1) from troops in major cities (e.g., New Orleans once the post office there was opened to civilians and thus had stamp stocks on hand), 2) troops in winter quarters, usually near large population centers, 3) static troops, such as those in garrison duty in the 20+ forts ringing Washington, DC, and, 4) soldiers who were sent stamps from home.

A number of government officials, Senators and Congressmen "misused" their franking privilege (with a wink from the post office, I suspect) in huge numbers. One was E.B. French, whose frank appears on dozens -perhaps hundreds -- of envelopes sent by soldiers in various units who were or had been in the DC area. I've read he did this as a favor when asked; however, the evidence suggests free-franked envelopes were handed out through various agencies as many were sent by troops from the field many months after they were last in the DC area.

As for what's more common, it depends on who and where. The Army collected mail and brought it to various postal centers to enter the 'civilian' mailstream. Mail from the peninsula campaign and campaigns in the • Piedmont area were brought to DC and to a lesser extent Alexandria for processing. Most seen from active campaigns was sent collect. However, because of the huge numbers of troops in the forts and camps surrounding Washington, many covers from the same period were sent pre-paid with stamps.

As Union armies occupied Vicksburg, Chattanooga,Nashville, New Bern(e), New Orleans, and other (primarily coastal) cities, civilian post offices were set up, stamps and handstamps provided and the government began servicing civilian as well as military mail. Again, there's a mix -- predominantly collect letters from troops in the field, predominantly stamped letters from troops who were more or less static for some period in and around the cities. This was especially true of New Orleans. However, a surprising number of field letters from troops on
Sherman's March bear stamps, apparently because he built reconstructed railroads for supply as he moved and stamps were regularly available to troops on the march.

What makes the SHIP ISLAND MISS postmark so collectible is that it is an intriguing anomaly. Butler brought a postal agent (who was attached to the Army -- rather unusual) with him on his invasion of Ship Island. The agent brought along (or had made locally) 2 handstamps (the circle and a more common straight line). They are thus quasi-postal service, quasi-Army markings. There are only a handful of such instances -- e.g., the Chattanooga Tenn straight lines, which exist in far greater numbers, and the Beaufort SC balloon circle handtamps, which are quite scarce.

What's unique is that the Ship Island handstamp apparently also saw duty in New Orleans on military mail (It was used on civilian mail, though if it was examples are very rare), and then was returned to purely military service on Ship Island.