“ Section 303 (e) of Executive Order No. 11157, as amended, is further amended to read as follows:
" (e) the term "field duty" for purposes of the third sentence of subsection (b) of Section 402 of Title 37, United States Code, shall mean service by a member when the member is subsisted in a Government mess or with an organization drawing field rations, and-
" (1) the member is under orders with troops operating against an enemy, actual or potential ”