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
42 || land firing nowhere (shells consumed)
46 | at ship out of range
48 | at sub, server pretends out of range
53 || land firing at bogus target
60 || land firing at undefended target
61 | 100% hat with one gun
66 | likewise one shell (take care to avoid automatic supply)
77 | at sector, fractional range, ~50% chance