• Obscured: Remove one die from your attack.
• Jamming Barrier: Remove half the dice (rounded down) from your attack.

Which order do you apply these penalties to your attack pool. If you have an even number of dice it makes a difference. For example a VSD-II shooting 6 dice at an obscured target through the jamming barrier.

Is it 6 dice halved to 3 then obscured down to 2 dice , or is it 6 dice obscured to 5 then halved to 3 dice ?

Is it that these two effects happen at the same time so it is the choice of the activating player in which case who would choose the order in a Salvo attack with 2 dice?

Both removing a dice for obstruction and removing dice for Jamming Barrier happen "before" rolling dice:

• Obstruction : "...the attacker must choose and remove one die from his attack pool before he rolls dice during the “Roll Attack Dice” step."
• Jamming Barrier : "... the attacker must choose and remove half of the dice from the attack pool, rounded down, before rolling ."

Then we go to the Effect Use and Timing part of the rules, which says:

• Effect Use and Timing : "... If two or more of a player’s effects have the same timing, that player can resolve those effects in any order."

So the attacker gets to choose which order to do these in. If there is an odd number of dice in the attack pool it does not make any difference, if there is an even number, the attacker wants to remove the obstruction dice first.

Ah, but isn't the Jamming Barrier effect a 2nd player effect as it's his objective?

9 hours ago, Formynder4 said:

Ah, but isn't the Jamming Barrier effect a 2nd player effect as it's his objective?

It is an effect, but it is not tied to a player. That would somehow imply that since the second player has to provide obstacles, they could somehow choose, or not choose, to resolve obstacle effects for either player...

The player conducting the attack can choose the order to resolve as mentioned by Grumbleduke.