Can you let me know where this comes from? Point defense is one of my main concerns, ...
Annatar Giftbringer said:
The point defense reaction is not an attack roll, and the laser to hit-bonus and fire control software specifically adds to attack rolls.
An attack is defined on p156:
When a ship attacks another [ship], it declares it is going to attack and selects a target.
This is just an extension of the ground combat rules on p71:
The most common Significant Action used in combat is to attack. An attack is an attempt to damage or injure an enemy with either a melee or ranged weapon, such as a knife or a rifle.
The Traveller declares he is going to attack and selects a target. The target may then choose a Reaction. The Traveller then makes an appropriate skill check and, as normal for any Average skill check, if he scores 8+, the attack is successful and damage is dealt to the target (see Damage on page 73).
The PD reaction is explicitly not an attack (p160):
Point Defence (Gunner)
Using a turret-mounted laser (beam or pulse), a gunner can destroy incoming missiles. Note that a weapon used for point defence cannot be used to make attacks in the same combat round, and vice versa.
The DM+4 for beam lasers comes from a table labeled (p156):
Common Modifiers to Spacecraft Attacks
The following modifiers are commonly used to influence Gunner checks when attacking.
They are not used for other checks or rolls.
Fire Control software gives bonuses to attacks
, and only attacks
Alternatively, it can give a positive DM to an attack equal to the listed number,
So, it does not apply to reactions, neither PD nor Disperse Sand.
Both Attacks and PD Reactions are resolved using skill checks with the Gunnery skill, so anything applying to Gunnery or checks in general would apply to both, such as anything boosting Gunnery skill or the chosen characteristic DM.