Current Doctrine
Submarines
USF 25(A)
Prepared By
COMMANDER SUBMARINE FORCE, PACIFIC FLEET
FEBRUARY, 1944
http://www.ibiblio.org/hyperwar/USN/...oct/index.html
Chapter 1, Section 2:
1222. While cruising on the surface in daylight, the highest periscope should be manned, as an additional lookout station.