No effective anti-air
No aircraft
No vessels

Land
• Seal (15mm)
  
• Walrus (15mm)

minor anti-air capability
4 aircrafts
1 vessel (low chance)

Land
• Seal (15mm, 30mm)
  
• Walrus (15mm, 30mm)

Air
• Albatross
  
• Razorbill
  
• Manta
  
• Petrel

Mantas and Petrels have a lower chance to spawn than Albatrosses and Razorbills.
Each aircraft will carry two from the following:
20mm, IR Missiles, Light Bombs


Turrets have a chance to spawn, and will appear with either a 15mm or a 30mm.


Vessels have a chance to spawn, but will be limited to one per island.
A Needlefish is more common to spawn in, but there is a rarer chance of a Swordfish being present.
Needlefishes will carry two from the following while sword fishes will carry all:
Cannon, IR Missiles, CIWS, Torpedoes

effective anti-air
4 aircraft
~4 vessels (max 5)

Land
• Seal (15mm / 30mm / 40mm / CIWS / IR Missiles)
  
• Walrus (15mm / 30mm / 40mm / CIWS / IR Missiles)
  
• Bear (Very rare chance, only one appeared once in testing)

Air
• Albatross
  
• Razorbill
  
• Manta
  
• Petrel

Mantas and Petrels have a lower chance to spawn than Albatrosses and Razorbills, but will spawn in more frequently than in 2 shield islands.
Each aircraft will carry two from the following:
20mm, IR Missiles, Light Bombs, Dumb Rockets, Torpedoes


Turrets have a chance to spawn, and will appear with either a 15mm, 30mm, 40mm, CIWS or IR Missiles.


Vessels have a chance to spawn, but will be limited to five per island.
Swordfishes are more likely to spawn and will almost be guaranteed on every island.
Vessel loadouts are similar to 2 shield islands.

effective anti-air and higher gun-calibers
4 aircraft
~5 vessels (max 7)

Land
• Seal (30mm / 40mm / CIWS / IR Missiles)
  
• Walrus (30mm / 40mm / CIWS / IR Missiles)
  
• Bear (100 Battle Cannon / 100 Heavy Cannon)

Walruses are more likely to spawn than any other land vehicle.

Air
• Albatross
  
• Razorbill
  
• Manta
  
• Petrel

Mantas and Petrels have a higher chance to spawn than Albatrosses and Razorbills.
Aircraft loadouts are similar to 3 shield islands.


Turrets have a chance to spawn, and will appear with either a 30mm, 40mm, CIWS or IR Missiles.


Vessels have a chance to spawn, but will be limited to seven per island.
Swordfishes are guaranteed on every island and spawn four per island on average.
Vessel loadouts are similar to 3 shield islands.

In order to get this information, I've sampled 20 islands from each island difficulty rating, Making it a total of 80 sampled islands.

All the data stated in this guide is from the sampling; inaccuracies may be present and any number of/percentage stated may be false.

My process of sampling included: Opening a new world while using the "Spectator Mod+UI" mod that is available on the workshop (Which made this a lot easier),W through islands and counting the number of enemies with their corresponding loadout.

Link to workshop mod:
https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=2988916145
Sampling data is available on this Google Spreadsheet[docs.google.com]

Hopefully this guide helped you!
Any feedback is appreciated.