I thought I knew the answer to this, but after the strange ruling on the Base Defense: Armed Station objective in the most recent FAQ, I realize I know nothing about how this game works.

My question: can a ship elect not to attack during its activation or is attacking mandatory (if possible)?

In the Learn to Play rulebook it reads "the ship can perform up to two attacks" which leads me to believe attacks are optional (as opposed to the wording under squadrons which uses "must attack"). However, in the Reference Guide under Ship Activation there is no "can".

My question has to do with Opening Salvo and withholding an attack so you don't waste the 2 bonus dice at long range or against the wrong target.

It's optional.

EDIT: Also for squadrons! Even for engaged squadrons.

As DiabloAzul pointed, both for ships and squadrons choosing to attack or not is optional. That word "must" you found in the RRG about squadrons is because if you decide to attack, you must attack an engaged squadron instead of a ship, but that doesn't mean that you must make an attack.

Wait, engaged squadron attacks are optional as well? Man, I should go back to playing checkers.

You can't imagine how many posts pages threads have been devoted to debating the fact that the operative part of that rule is "rather than an enemy ship" .

Long after the guy who wrote the rulebook explicitly explained this.

Exactly. For more refference I think that this works:

• When a squadron is activated during the Squadron Phase, it can move or attack, but not both.
• When a squadron is activated by a O command, it can move and attack in any order.

It never says in the Rulebook that it must move or attack.