Major Alternate Paths: Revive the Old Confederacy as the United States and provoke a new civil war, or hasten decolonization of the British Empire.
Ship Design: Research new components and refit older vessels to take advantage of new knowledge. Outfit your submarines with snorkels for improved stealth.
Admiral Traits and Skills: Tailor and level up your Admirals with new traits and skills.
Governments in Exile: Welcome a government in exile to your democracy, boosting their legitimacy in return for more manpower and elite troops fighting to free their homeland.
Other National Focuses: New national focuses for The Netherlands, United Kingdom, Mexico and USA
Naval Mines: Protect your coasts from invasion or assault with anti-ship mines, or sweep a clear path through enemy mines before the fleet makes the big push.
Shipping route controls: plot new routes for your shipping and navies by toggling individual sea regions to limit or ban shipping there entirely.
Naval Treaties: Struggle to keep the peace by following internationally agreed upon rules, or creatively defy the world consensus by exceeding your limits.
Amphibious Landing Vehicles: Add power to your beach landing by researching and producing specialized combat vehicles for your marines.
New Music: Original music composed specifically for the Man the Guns expansion.
Fuel - a new resource that mechanical units consume.
Different types of naval terrain, that can modify naval combat in different regions.
A completely redone naval combat system
Gameplay rules - a large amount of options to further customize gameplay experience and make organizing multiplayer sessions easier.
Updated map-modes - new map-modes and a new configurable quick access system (a lot like in EU4).
70 new releasable tags added to the game to enable decolonization as well as a variety of map changes - more states in places like west Africa, and more accurate states like East Bengal/Bangladesh, and more.