too easy this game. once you have the police car you can complete all games on the first attempt. I suggest making the non-red cars slow you down more when you hit them, to add more challenge. Maybe you can give an adjustable difficulty setting.
the reason I don't recommend subs is that too many units can take them out and they don't attack air units. Bombers do the most damage of any unit in the game, and as long as you have aircraft carriers as support, the AC planes will take out subs/ships and protect the bombers. 4 frigate will take out a nuclear sub. Do the math, cost-wise 4 frigates are a fraction of how much a nuke sub costs.
just beat last boss Yamamoto first attempt - TIP : max out all factories first, while building frigate and cruiser when you see flyer or sub. Never build subs or nuclear subs. After you max out the factories start building manual cannons. Then build fortress (if you have it). Then put manual cannons on the fortress. Then wait till your resources are max (while building frigate/cruiser as needed. Then build 2 aircraft carriers and build bombers. Keep building bombers. When AI sends massive aerial counter-attack, then build fighters, till air dominance is achieved. Then build aircraft carriers and bombers until game is won. Simple.
I just beat the game in one play through.. Rogue is pretty OP .. but last mission to slay 5 councilmen took a few attempts. I never needed to buy any bodyguards. Just dump all rogue points in Dexterity and it sends your crit rate through the roof and your ability to stealth is sped up dramatically. From the sounds of it playing as Phoenix is easier then playing as Guardian since you only have to face 1 final boss and not 5 councilmen with 50k total life. Save game sounds like it might be bugged but I never had to use it so I don't know. As rogue use stealth followed by stun followed by smoke and hit space and rage potions .. that's all you need.
there are some serious bugs with this game. I lost connection just now and on reload lost 3 blood walls that I purchased and it reset my decks, so I lost a deck I built yesterday, as well as other cards are missing
 "New Star Soccer"){kind=icon}
 "Legacy of a Thousand Suns"){kind=icon}
 "Neon Race 2"){kind=icon}
 "Fairway Solitaire"){kind=icon}
 "Racing Comrade!"){kind=icon}
 "Arcuz (Full Version)"){kind=icon}
 "Black Navy War"){kind=icon}
 "Hands of War 2 - Expanded Edition"){kind=icon}
 "Elements of Arkandia"){kind=icon}
 "Space Arcade (the game!)"){kind=icon}
 "Zomgies 2"){kind=icon}
 "Hack Slash Crawl"){kind=icon}
 "Tyrant"){kind=icon}