In this mission there is a nearly symmetrical map with you on the left and the enemy (Blue) on the right. Blue has a slight advantage in units (an extra tank and sub), slightly more starting cash, and also a significant advantage in resource (oil) production: Blue starts with the equivalent of 12 refineries and can easily increase to 14 unopposed, whereas you start with the equivalent of only 4 refineries and can only grab another 3 without serious opposition. So in effect Blue has twice your resource income each turn. Correcting this resource gap is critical, otherwise you will be ground down in a war of attrition.
While you could fight over the oilfields in the center of the map, that is likely to be futile as they are protected by Turrets on both sides and are in difficult terrain. Much richer pickings can be found on the uncontrolled islands to the north. If you can take the facilities on those islands you can equalise resource income and take that advantage away from the enemy.
In this mission you have Albatross Air Transport capability (which costs only 20 points per unit). Use this to deploy your infantry (commandos) rapidly and seize facilities. You may want to build a Raptor to protect the units while in the air. The enemy often builds Raptors, even if you don't.
Meanwhile you need to maintain control of your part of the southern landmass, and take control of the sea. If you can control the sea you will be able to take the northern island with its 2 Advanced Refineries (each one equal to 4 normal refineries) and should then easily win.
To hold your ground in the south, move your tanks forward to control your chokepoints at the north and south edges of your half the southern landmass. You may need to switch between them if Blue changes his line of attack. The chokepoints are north and south of your Air Control. The northern chokepoint is the first and second tiles in from the north coast (or the two tiles west of there if you prefer). This chokepoint is harder to defend as it is broader, two units high. Naval support or artillery may be helpful. The southern chokepoint is a single road tile at the bottom of the map. As Blue has an advantage in tanks (3 to your 2) you may need to build an extra tank early on, in order to hold both of these chokepoints. Remember to make good use of your Turrets. Don't advance further than one square behind the max range of your Turrets, so that when your chokepoint tanks are engaged, your Turrets will be able to fire on the attacker.
On the sea this is classic naval warfare. Subs are decisive. Use your Hunter to find the subs, and your own sub to kill them off. Evade the enemy Corvette Fighters until you have dealt with his subs. Once the subs are dead you have no threats and your sub can clear the seas with impunity. If you control the sea you should win the game. However if you are smart with the use of airmobile units you will already have seized the facilities on the northern island before you have won control of the seas.
Here is showed where each of the U-Boats are located:
Note from Machow8 (also know as Thopson1m/Arkium): they could be find thanks to game files' data.