I'm guessing stationary will be in-vogue again.

5-50. A censorship policy of detainee mail may be instituted by the theater commander as follows:
z Outgoing letters and cards may be examined and read by the detention facility commander or a
designated representative.
z Mail will be returned to the sender to rewrite portions that contain obvious deviations from
regulations, and a copy will be provided to the supporting counterintelligence element.
z Outgoing letters and cards will be sent, unsealed, directly from the facility to the theater
commander’s designated censorship element. All incoming letters and cards that arrive at a
facility without having been censored will be sent to the designated censorship element before
delivery to detainees.
Chapter 5
5-10 FM 3-39.40 12 February 2010
5-51. Letters and cards addressed to persons other than representatives of a protecting power or to U.S.
military authorities will not—
z Contain complaints or criticism of any governmental agency or official.

This could apply to war OUTSIDE the U.S. I guess.