We do not know of any prohibition in the 5000 series documents that would prevent two separate services from working together and sharing documents, funding, supportability approaches, etc. as it has been done many times in the past (well below the declared joint-program level). Not sure if the Navy LSCP requirements would be an exact match to the Army's requirements, so there may be a requirement for some Army-specific annexes. Also, there may be separate service-related policy that provides more information on this types of activities. In any case, there would need to be some memorandum of agreement or understanding delineating who is responsible for what, when, and how and signed by both Services (at the very least at Milestone Decision Authority Level).