NATIONAL ENSIGN The following rules govern the display of the national ensign in port and under way. In  Port When not under way, commissioned ships display the ensign from the flagstaff at the stern and the union jack from the jackstaff at the bow from 0800 to sunset. In the case of a mastless ship, the ensign will be displayed  from  the  loftiest  hoist  on  board.  After entering a foreign port during darkness, a Navy ship briefly displays the ensign from the gaff at first light to establish nationality. Other ships of war present customarily display their ensigns in return. According  to  SECNAVINST  10520.4,  the  oldest ship in the Navy, as identified by the Chief of Naval Operations, is to display the first Navy jack, in lieu of the union jack, at the jackstaff. Under  Way When flown under way during peacetime, the ensign normally is displayed during daylight from the gaff (or triatic stay in the case of those ships with mast-mounted   booms   and   stays,   which   would interfere with the hoisting, lowering, or flying of the national ensign) under the following situations unless otherwise directed by the senior officer present: Getting under way or mooring/anchoring Falling in with other ships Cruising  near  land When  engaged  in  battle When cruising under wartime conditions, it is customary to fly the national ensign continuously at sea, since battle action may be regarded as always imminent. The union jack is not flown under way except in the case to denote a general court-martial or court of inquiry is in session. In that case, it is flown from a signal yardarm. Size of Ensign/Jack for Shipboard Use Table  10-l  shows  the  appropriate  size  of  the ensign  and  jack  to  be  used  aboard  your  ship. Remember that the union jack must be the same size as the union portion of the ensign being flown from the flagstaff. Shore Display of the National Ensign The national ensign is displayed from 0800 until sunset at all U.S. naval activity headquarters. The following are additional rules that apply to the display of the national ensign: No other flag or pennant will be displayed above or, if on the same level, to the right of the ensign. Table 10-1.—Sizes of Ensigns and Jacks for Shipboard Use LENGTH HOLIDAY DAILY SHIP FLAG JACK S ENSIGN JACK S ENSIGN JACK STAFF STAFF I DIMENSION DIMENSION I DIMENSION DIMENSION Z Z E E Less 100' 10' Jackstaffs  with 8 3'6" 1' 10 9/16" 10 2' 4 7/16" (See Note 1) anchor  lights 6' 7 3/4" × × × mounted  thereon 2' 7 5/16" 4'6" 100'-150' 12' shall be of sufficient height 8 3'6" 1'  10  9/16" 10 2' 4 7/16" (See Note 1) so as to conform × × × to Rules of tbe 6' 7 3/4 2' 7 5/16" 4'6" 151'-200' 15' Road 7 5' 0" 2' 8 l/4" 8 3'6" 1' 10 9/16" × × × × 9' 6" 3' 9 5/8" 6' 7 3/4" 2' 7 15/16" 201'-450' 17' 7 5' 0" 2' 8 l/4” 8 3'6" 1' 10 9/16" × × 9'6" 3' 9 5/8" × 6' 7 3/4" 2' 7 15/16" 451'-UP 22' 5 8' 11 3/8" 4'  9  13/16" 7 5'0" 2' 8 l/4" × × × × 17' 0" 6' 9 5/8" 9'6" 3' 9 5/8" 10-2