Shark Assault Boat
The Shark Assault Boat is the Imperial Navy's run of the mill assault boat. At around 55 meters, the Shark Assault Boat is ridiculously huge, being around as long as either a Warlord or Imperator Titan is tall. This size is meant to carry an equally as ridiculously large troop cargo bay. The Shark consists of a large engine and an armoured troop compartment that is studded with magnetic clamps and Melta Charges which than be used to breach a ship's hull and blast a fucking hole into it (Quickly vaporizing any poor mook standing in front of the Melta Charges) before unleashing its full cargo of assaulting Imperial Redshirts. Due to their role, nearly all Sharks can carry only defensive weapons with most of the space within the hull dedicated to armour, engines, or carrying capacity.
Tactically, Sharks are often accompanied by fighters to help the assault craft breach an enemy vessel's defenses without getting shot to pieces. Additionally, their size means that the Sharks are never seen on anything smaller than a Battleship-sized carrier, and even then only at significant cost of space and efficiency.
Battlefleet Gothic Armada
In Battlefleet Gothic: Armada, the Shark Assault Boat is the mainstay boarding vehicle for both the Imperial Navy and Space Marines. Usually Shark Assault Boats like other boarding vehicles are a coin flip. If they fail to succeed in boarding, they simply blow up or crash into the enemy ship. If they do succeed however, the crew members of the Shark Assault Boat can do a unholy amount or rape and mayhem to your target.
Usually the enemy ship often have one of their turrets destroyed, engines disabled, hull breached or the entire ship being set alight. Usually the crewman of the Shark Assault Boat dies in the end, but at least they die happy after severely crippling the enemy as an army of Spess Mehreens and roided-up Catachans start to throw melta bombs everywhere that is vulnerable looking.