Changes are coming to transports in Warhammer 40k 10th Edition. Ever since its announcement at AdeptiCon, Games Workshop has been drip-feeding new information about the latest edition of their grimdark sci-fi miniatures war game. This has included new rules for building an army as well as increasing the toughness of vehicles, all under the new slogan of "simplified, not simple." Now, this same design mentality will be affecting how your soldiers will get to the battlefield and how they will strategically retreat.
Warhammer 40k 10th Edition transport changes
According to an official Warhammer-Community post, the following changes to transport rules will be coming in Warhammer 40k 10th Edition. In earlier editions, only certain units were allowed to exit a transport on the same turn that it moved. Now, any embarked unit is free to exit once a transport has moved. The only restriction is that if the transport Advances or Falls Back, that unit can't exit. Units can also shoot, but cannot charge unless they exit the transport first.
For armies with a lot of vehicles and mechanized units, this is a big improvement for Warhammer 40k 10th Edition. While units cannot embark and disembark on the same turn, it does mean that vehicles aren't spending an entire turn spinning their wheels.
As for how units will fire from within these vehicles, that is being consolidated under the universal Firing Deck X rule. Just choose one weapon each from a number of embarked units models and the transport will count as if it's equipped with them for shooting attacks. For example, a Chimera tank has Firing Deck 2, so you pick two Cadian Shock Troops with a plasma gun and a meltagun respectively. This also means that, since the transport is the one making the attack, the weapon attacks gain any boosts the vehicle does.
Of course, there will be some exceptions to this rule. Fast-moving vehicles like Astra Militarum Taurox can disembark troops even after advancing. The Space Marines' Land Raider reclaims its Assault Ramp ability, meaning units can declare a charge on the same turn they disembark. Astra Militarum Chimera tanks now have Mobile Command Vehicle, which will allow Officers to issue orders while inside the (relative) safety of the tank. Lastly, the Aeldari Falcon gray tank can issue Fire Support, allowing any units that attacked after disembarking to re-roll any Wound rolls.