A few specialist suggestions...
Spartan: Sub limit is 300 regardless of energy output. In combat, your Drillers deal half their strength in damage (rounded up) before specialists participate.
TONIGHT WE DINE UNDERWATER!
Note: I was trying to think up of a good character that can rival the King. The King compensates for destroying Drillers by preventing Shields. This specialist, the Spartan, compensates for extra damage by setting the sub cap to 300, regardless of any generators or other specialists you own. At first the specialist appears to be overpowered (something better than a King, for the cost of one promotion!), however the Spartan is designed for survivability in small spaces, kind of like the Spartans in a movie we prefer to not talk about. Therefore, as territory gets larger, the Spartan becomes less and less of an option. Still, while it is designed as an early game character, even for those who have reaped the reward of high sub cap limits it is an excellent endgame character as well.
Gift-Bomb: Cannot be seen by other players. Detonates inside owner's sub six hours after being gifted - blast radius is 15% normal sonar radius. Detonation is cancelled and ownership converted if another player takes ownership of the gift bomb first.
We sell gift horse bombs too. Now available in Trojan!
Note: This one is clearly based off the Martyr. The difference here is that the gift-bomb adds a psychological element. Since no one can see a gift-bomb, only people who can see the player's Queen can know whether you have a gift-bomb or not. Making a gift-bomb work successfully on a Queen also becomes a matter of whether the enemy knows about the gift bomb or not. In other words, as a stealth Martyr it will alter the enemy's behaviour, and how it will deal with attacks from the player's border - essentially changing up how the game is played in the process.
Leper: Any outpost Leper touches becomes infected with a disease that destroys 1 Driller every hour at outposts or subs where infection occurs. The disease can be also be spread through subs travelling from infected outposts. Infected outposts with no Drillers are cured, and become neutral buildings with full shields.
There's no death like a black death.
Note: This specialist was specifically designed to make the player be as much a threat to other players as he is to himself. In return for an outpost's inability to provide friendly support in a battle, the outpost becomes infected with a disease that can pose problems to even Tycoons. Anything with disease will "blink" (disappear and reappear at half-second intervals), and clicking on the blinking sub or outpost will show "-1 Driller in 0:45 and every 1:00". The only way to prevent infection by a diseased sub is to destroy it before it arrives, and even in doing so you sacrifice your own soldiers to get rid of it. So yeah, the death thing goes a long way with this one.
Physicist: Blows up an outpost you control upon command. Blast radius is outpost's current sonar range.
Neptunium? I thought you wanted Uranium!
Okay, so this one is clearly designed as a bigger Martyr, only this one isn't built to participate in combat. So, since most outposts a player owns can see at least one other owned outpost in the vicinity, the Physicist is built to be a big bomb that would be difficult to detonate without sustaining losses of your own. 'Nuff said.
Surveyor: +1 Neptunium every 2 days for every building you have while at an outpost.
Most things can be found easily. One need only know where to look.
This one is built to be a mobile mine that bypasses sub payment for the cost of a smaller mine that can move around (albeit at the cost of potential Neptunium.) This specialist is designed not to be a replacement for an actual mine, and more something that can help grab a higher place in rankings at the last moment.