Submarine Alliance

"Join forces with the Monkey Subs and defeat the ZOMG bloon. Doing so will unlock the Monkey Sub for use in your city!"

- Bloons Monkey City Mobile level description Submarine Alliance is a special mission that is only available in Bloons Monkey City Mobile. There are 4 1/1 Subs defending a broken 2/4 Sub. The player's job is to repair it for $8000. There isn't much land or track in either direction and there are 15 rounds, so good luck. Also this mission internally starts at Round 4, so harder bloons come early. There's a ZOMG at the end, hence the urgency to repair the 2/4 sub, but there are also MOABs in the way. Bloons travel towards the broken Sub at the middle with 2 paths. Also, the ZOMG is not the only bloon in round 15. When reaching round 15, players should get correct timing to destroy the ZOMG otherwise the player will lose. You can also set the 2-4 sub to prioritize Strong to ensure that the ZOMG gets hit. Completing this tile earns 500 XP, at least 200 and 5.

General Notes
Round 14 and 15 are by far the hardest in the mission, with possible MOAB spawns on round 14 and with a ZOMG, multiple MOABs and loads of ceramics on round 15. The best way to beat it is to ignore the ZOMG and put all funds into defenses to destroy the other bloons (which are much faster). The ZOMG will be the only bloon remaining, and so all the other towers can be sold to repair the submarine and instantly destroy the ZOMG. This also removes the risk of the First Strike missile hitting the wrong bloon. A much easier way to remove that risk is to put the targeting of the Sub to strong and fire at the ZOMG when there are no bloons in the way. The best possible scenario is to fire the missile when one of the round 15 MOABs is over the ZOMG, which will destroy both the MOAB and the ZOMG (as shown in some YouTube videos).

Qwertyxp2000 the second's Spike Factory-Apprentice strategy
I had started off with $3850 cash. I put one Spike Factory on each side as 1/0. Then I added an 0/1 Monkey Apprentice with my spare cash. Then I added one more on the other side. Try to upgrade the Apprentices to 0/2 then 2/2. Upgrade the Spike Factories to 2/2, 1/2 first. Invest for $8000 to repair the damaged sub. (Or use Banana Farms to invest if you wish.) Then save more money and wait until Round 14.
 * Plan A

During Round 14 there was a MOAB going left, at least in my Special Mission. Invest some more cash during the round (but preferably before, if enough cash), get a MOAB Assassin and use the ability to destroy the MOAB layer that would frustrate the defenses. Do it as soon as possible which otherwise would overwhelm the Spike Factory. Use the other defenses to get rid of the other bloons and ignore the ZOMG. Then use the First Strike Capability to destroy the ZOMG.

Do the same thing, except after upgrading the two Spike Factories to 2/2, sell the Monkey Apprentices when the amount of cash reaches $5600, which then means you can repair the sub earlier. Perhaps also use Banana Farms to invest too, if you wish.
 * Plan B

During the time, I had Monkey Knowledge Packs with the capability of selling towers at 85% price. I also had all 2% discount of all base tower costs and 1% discount of all upgrade costs. I also had Monkey Apprentice base attack speed and Fireball speed increased by 5%. The Spike Factories had one extra spike per pile and 3% discount of all costs. The Bomb Shooter has $100 discount on Bigger Bombs and projectile speed increased by 10%. As for the Monkey Subs, they have a 15% increased projectile speed and 3% increased range.
 * Other notes

Although I am not sure about Round 15, I hope the other parts of the strategy will inspire you readers.

In fact, my friend completed this mission for me. My friend put in 1/0 Spike Factories and some Boomerang Throwers in the first round. By Round 14, he has a Monkey Pirates at the center, two 3/2 Spike Factories, one at each end, some Glaive Riccohet and Bionic Boomer with Glaives, and the fixed center submarine. He used MOAB Takedown to pull down the single MOAB on the left. In Round 15, he used the First Strike Capability to destroy the ZOMG on the left. The left MOAB was destroyed with all of the helping towers on the left, while the right had enough supporting towers to destroy that side's bloons.
 * Conclusion

Strategy by Anonymous (doesn't work even with 3600 starting cash. Lost just after upgrading spike factory to spiked ball on round 13)
Started with 3400 cash. First put two 1-0 Spike Factories, one on each side. As Round 1 starts, buy two boomerang throwers. Upgrade them to 2-2.Next,upgrade the Factories to 2-2.Then buy a 1-1 apprentice to deal with leads(regen.).Then when you get enough cash, get 6 bomb towers. Upgrade to 2-3.Then upgrade the boomerang throwers to 2-3.Then upgrade the factories to 3-2.(really important!).All this should be done by round 14.During my mission, there was first an MOAB coming on the left, and then one on both the lanes. I dealt with that using a monkey boost(one lasted for both MOAB) rushes. Before Round 15 sell the Spiked Ball Factory on the left and the apprentices. Then repair the sub. On Round 15,The MOAB Rush pattern was repeated, with the first on overlapping the ZOMG. Destroy the ZOMG and the MOAB with First strike, and buy back your 3-2 Factory. Then use Monkey boost again to destroy more MOABs.

''Tip:Make sure you got some free monkey boosts.It really helps in avoiding spending bloonstones. ''

ChickenBandit's Strategy

''Start with a supply crate. Place 2 0-3 dart monkeys on each path''

Introduction
I attempted this mission when I was at Level 16. This was quite difficult and I beat it with only 5 lives remaining. But this is a quite effective method.

Towers Needed

 * Two 2/1 Spike Factories
 * Four 2/3 Dart Monkeys
 * Two 2/X Glue Gunners
 * One 1/1 Sniper Monkey
 * Two 2/2 Wizard Monkeys
 * Two 2/X Ninja Monkeys
 * Six X/3 Bomb Shooters
 * Three 3/X Monkey Buccaneers
 * Two 2/X Engineer Monkeys

Walkthrough

 * Place 2 Spike Factories and 2 Dart Monkeys and the top and bottom ends of the islands. Place a 1/X Sniper on the right island and set it to strong.
 * At Round 2, place two more Dart Monkeys near the others. Upgrade 2 to X/1.
 * Until Round 4, try to upgrade all four Dart Monkeys to X/3.
 * At Round 5, place two X/2 Glue Gunners.
 * At Round 7, upgrade the Sniper to X/2 and Spike Factories to 2/X. The Spike Factories are utmost vital for the Lead rush.
 * At Round 8, place 2 Wizards and try to upgrade them to 1/X. Set their targeting to strong.
 * At Round 9, place two 2/X Ninja Monkeys.
 * Then keep saving $8000 for the Sub. You would probably be able to repair it on Round 11.
 * Put two X/3 Bomb Shooters on both islands. Then place two 2/X Engineers, one on each island.
 * Round 14 is quite dangerous, so upgrade the Wizards to 2/X
 * Try not to Fast Forward Round 15. Firstly finish of the ZOMG with the First Strike ability. Then place two 3/X Buccaneers. And place 2 more X/3 Bomb Shooters.
 * Hopefully you'll finish this mission with only 90 lives lost ;).

Trivia

 * Apart from the ZOMG, the bloons sent vary, much like a normal tile.
 * The ZOMG is the first bloon in Round 15 only coming from one side, but later in Round 15, multiple MOABs come out.
 * The 4 1/1 Subs cannot be upgraded in an initial playthrough of the level (as no research of the subs has been unlocked).
 * They can be upgraded if the player replays the level through the "My Tracks" section.
 * They still cannot be sold, however.
 * There are Regen and Camo bloons in this level. When they come and what type they are is different for everyone, because Bloon Spawns vary.
 * It is possible to lose no lives without spending any cash on Round 1. However, as all bloon spawns will vary, only lucky ones may lose no lives without spending any cash on Round 1.
 * Completing this mission leaves no trace of on your city map leaving a normal captured Lake tile in both appearance and function.
 * On the mission's info screen, the length of the mission before was 26 Rounds. Later on, the length was shortened into 15 Rounds.