Advanced Propulsion is a technology that can be researched at the War Center in Tech Level 4. It costs 500 Food and 300 Nova, and gives Ships +15% speed. It is available to the Gungans, Royal Naboo, and Trade Federation.
Like most naval upgrades, this technology is vital on water maps, and useless on maps where naval combat doesn't play an important part.
"By researching superior underwater propulsion systems, you can cause all your Ships to move considerably faster thanks to this Tech Level 4 upgrade."