The extremely long playing time of the campaign scenarios (using weekly turns) make it somewhat of a mini-monster. The game was indeed complex for 1971, but not so much now when compared to other games on the Pacific Theater.
The vassal module available at Consim Comment conforms to our typical approach of providing mainly just the map and counters. You will need the printed rules, tables, and air mission logs (or PDF versions).
The published components for U.S.N. were constrained to what the medium (S&T magazine) could accommodate. For example, Naval Air counters were left off the counter sheet because it only had room for 400 counters. SPI provided a work-around with Naval Air Strength Charts for each side. These are dispensed with in the vassal module, which provides actual Naval Air game-pieces.
The size of the printed map was limited as well: only the hex-grid playing surface is depicted. The charts, tables, and tracks one typically sees on an SPI map are relegated to the rule book.
U.S.N. is known for its tall stacks of counters. The module gives each side a "Forces" map window to allow stacks to be spread out. "Datum" tokens are available for assignment to each such force and these are placed on the map instead of fiddling with tall stacks. Each Datum token is given its own unique letter or number using the right-click menu.
You will still need to do some bookkeeping on paper (as in the printed game) to keep track of ship fuel status, damaged ship repair times, and victory points.
U.S.N. is a perfect example of what SPI was about in 1971. Functional, blue-print like, graphics. Game-play centric. Expanding wargame topics well beyond the offerings of Avalon Hill - the 800-lb gorilla wargame publisher at that time.
See also: Solomons Campaign for an operation-focused refinement of U.S.N.
U.S.N. Module Notes
Land and Air units are found in the Pieces palette. Naval units are found on each player's Forces map.
Forces maps can be used in any manner the players see fit to mitigate unwieldy stacking on the map. There is a generic "Datum" game piece in the Pieces palette for identifying groups of units. Use two Datum markers for each force: one on the Forces map and another (having the same identifying mark - i.e. a letter or number) on the main map.