Hey Dai,
You have two choices...this is taken right from the Ships-2 manual, June '42 Revision Supplement. There has been some talk that some US subs may have carried Measure 23, but I've yet to find any evidence of it... Jeff
Ms 9: Black System for Subs. Vertical Surfaces:
Paint entire submarine above the waterline black, formula 82. The painting shall be carried over all parts which are visible for the air including the numbers, capstan and running light boards and bridge rails. The radio insulators shall be dark. There shall be no boot topping. The underbody shall be painted with the current issues of bottom antifouling paints.
Horizontal Surfaces:
All horizontal surfaces except wood decks shall be painted Dark Gray 5-D. The systems differ only in the painting of the vertical surfaces. In case of doubt, as on sloping surfaces, use Dark Gray 5-D.
Notes:
The camouflage painting need not be exact or carried into corners. Small gear, wires, rigging, and areas permanently in shadow, as under boats, etc., need not be painted with the camouflage colors. There is no objection to exact or careful painting which may be desired for the sake of good appearance at close range.
All bright or shiny objects, no matter how insignificant, shall be painted, covered, or removed.
Glass windows shall be covered or removed, especially during the day in sunny weather, and at night when anticipating searchlight discovery. Insofar as conditions permit, similar precautions shall be taken on airport lenses.
Ms 10: Gray System for Subs. All Surfaces:
Paint entire submarine above the waterline Ocean Gray 5-O. The painting shall be carried over all parts which are visible for the air including the numbers, capstan and running light boards and bridge rails.
The radio insulators shall be dark. There shall be no boot topping. The underbody shall be painted with the current issues of bottom antifouling paints.
Notes:
Exposed brightwork shall be painted to harmonize with the exterior of the ship.
All Glass windows shall be removed, rolled down, or covered, unless conditions are such that light reflection from their surface is unknown. Insofar as conditions permit, similar precautions shall be used on airport lenses.
All Canvas covers shall be colored to match adjacent ship paint.
Raised characters, such as ships names and draft marks, shall be retained and painted the same color as the hull in that vicinity.
Decks were NOT painted 20-B, but the hull color.