What's a Mercruiser "Power Shift" ??

[Glassparman]

I was just given a 1974 26' Fiberform with twin Mercruiser 165's.<br /><br />I'm new to the I/O world and I'm looking under the back deck at the motors. <br /><br />I see this cylinder thingy with shifter cables going in and out and a hose attached. It says is a Power Shift.<br /><br />What the heck is that??<br /><br />Thanks in advance,<br />Michael