2 | land must have mil>0, glim>0, gun>0, shell>0, eff>=40, and not on carrier
17 | at sector that doesn't exist
19 | at ship that doesn't exist
21 | at valid target, but no mil
45 || land firing nowhere (shells consumed)
49 | at ship out of range
51 | at sub, server pretends out of range
56 || land firing at bogus target
63 || land firing at undefended target
64 | 100% hat with one gun
69 | likewise one shell (take care to avoid automatic supply)
80 | at sector, fractional range, ~50% chance