Well, many have been watching how the game is dying and the main reason I can come up with is because the game at low levels is quite monotone and you can't really get the satisfaction of sinking a surface ship (Unless you play Blitzkrieg and spam spam sapm in Hobbit wars)
My Suggestion would be simple: Create a new game mode where players can face off against a really hard AI oponet (I.E: A Baram, 10 BB123456 depending on level of the players and so on), this would be kind of a "Boss game mode" where players will have to actually do some teamwork in order to defeat the AI boss.

For the Exp reward: Give a fixed experience for defeating the enemy, the harder the enemy, the better exp. Give same exp for all players that participated in the game and actually helped to defeat the enemy (Be it by downing it's scouts, directly atacking it, or just droping mines).

Also, a small random reward would be nice for new players (Expert boosts, some extra credits, Mines and stuff like that) But PLEASE DON'T GIVE PHH AWAY!