Pegasus Amphibious Assault Vehicle
The oddly named Pegasus Amphibious Assault Vehicle otherwise known as the Pegasus AAV or simply the Pegasus, is one of the few truly amphibious vehicles of the Imperial Guard with the exception of the Chimera of which the Pegasus based its chassis upon. It is oddly named due to the fact that normal folks associate the Pegasus as a flying mythical creature, a more accurate name would have been Kelpie, but oh well. Eh, hippocampus is the water version of Pegasus.
The Pegasus AAV is a converted Chimera variant designed by the Adeptus Mechanicus during the battle of Death Bridge on request of General Strong, in order to quickly cross the mile-long river under the bridge and flank the Chaos forces holding the other end. The newly-created vehicle proved very effective in its role, ultimately winning the battle, and General Strong's ingenuity still being talked of in all the Baine regiments.
The Pegasus saw widespread use afterwards, and is often found in Imperial Guard support divisions to this day.
The Pegasus uses a layout similar to the Chimera's, up to the turret and lasgun array, with a few exceptions: The vehicle possesses two access ramps for faster unloading, one at each end, at the cost of hull-mounted weaponry. The vehicle has been equipped with floats on its sides and the armor has been reduced in order to further improve floatability, making the Pegasus more vulnerable but also faster and cheaper that the Chimera.
The reason why you don't hear that much from the Pegasus is due to the fact that it shares the name of two other different vehicles all from the same faction. The other two Pegasus are called the Pegasus Armoured Fighting Vehicle and the Command Vehicle variant, as such it has very little to do with the AAV. For much added Derp, in Citadel Journal #15, both the AFV and Command Vehicle was renamed the Centaur and Minotaur AFV respectively. This was later changed to avoid further confusion with the Centaur Utility Vehicle and the Minotaur Artillery Tank, which really goes to show the absolute clusterfuck that was, early GW.