2 | land must have mil>0, glim>0, gun>0, shell>0, eff>=40, and not on carrier
20 | at sector that doesn't exist
22 | at ship that doesn't exist
24 | at valid target, but no mil
48 || land firing nowhere (shells consumed)
52 | at ship out of range
54 | at sub, server pretends out of range
59 || land firing at bogus target
66 || land firing at undefended target
67 | 100% hat with one gun
72 | likewise one shell (take care to avoid automatic supply)
83 | at sector, fractional range, ~50% chance