to sum it up:
1. am vessels conduct hit and run attacks normally. boardings + hit and runs AGAINST am vessels may reroll result once. second roll stands.
2. may not use boarding torpedos or assault boats.
3. all am vessels increase turret value by 1
4. every am vessels (excluding light cruisers) has an extra 60cm left/front/right dorsal lance
5. light cruisers Endeavor and Endurance may replace torpedos for 30cm dorsal lance left/front/right at no cost
7. all cruiser with prow armour value 6+ may replace their torpedos with nova cannons for +20pts, retibution class battleships may do this for +10pts
8. all 30cm weapon batteries in your fleet may be increased to 45cm for +10pts per battery pair
9. all am vessels armed with torpedos may use refitted torpedos from the armada rulebook. battleship +30pts, cruisers +20pts, light cruisers +10pts
10. am vessels may take ld tests to fire upon own hulked vessels to prevent the loss of precious tech to the enemy
11. every am vessel makes a roll on the omnissiahs gift table:
1 Emergency Energy Reserves: When crippled, the ship
only reduces turrets, shielding and weapons by 25%
rather than 50%. The vessel still counts as crippled in
every other respect.
2 Advanced Engines: The ship gains +5cm speed, as well
as +1D6 when on All Ahead Full special orders.
3 Repulsor Shielding: Ignore all negative effects of having
a blast marker or gas clouds in contact with the ship's
base as it applies to leadership, movement and
repairing critical damage. This effect goes away if the
ship suffers “Shields Collapsed” critical damage.
4 Fleet Defense Turrets: Up to two turrets on the ship are
exchanged for fleet defense turrets capable of
protecting itself or any one other vessel within 15cm
each ordnance phase, adding +2 to the turret strength
of the ship it is defending (this does not alter bomber
attack rolls when used to defend another vessel). These
otherwise work exactly as normal turrets do in all other
5 Gyro-stabilized Targeting Matrix: Ship weapons are
reduced to 75% instead of 50% when on All Ahead Full,
Come To New Heading or Burn Retros special orders.
Nova Cannon still cannot fire.
6 Augmented Weapon Relays: Weapon batteries shift left
on the gunnery table before all other modifiers are
applied. Lance hits count double on rolls of a 6.
reroll any non apllicable refit
12. am fleets may not use heavy/battle cruisers
13. leadership: 1= Ld 7. 2-3= Ld 8. 4-6= Ld 9.
14. quest for knowledge.. even more additional stuff.. i won't copy it here. it's too much.
so these buggers are pretty powerful.
you can find it all in the (and costs for the ships)
Vessels of Mars: Ships of the Adeptus Mechanicus file, where the arc is also described