It's always been wrong for ships, and land units were changed to match
ships in lndsub.c rev. 1.49.
the offense strength.
.s1
Fort, ship, and unit support is simply those forts, ships, and units
-in range that can fire (see info fire). Note that ships and units on
-missions will not fire support. Plane support comes from
+in range that can fire (see info fire). Plane support comes from
those planes on "support" mission. The support multiplier is
.NF
1.0 + fortdamage/100 + shipdamage/100 + planedamage/100 + unitdamage/100.