Rocketmen or Blasters, whichever you want to call them are a great unit for plundering (the act of stealing resources from other players) as these units deal bonus damage to walls and the amount you plunder is based on the amount of damage you deal to said walls. Blasters also excel at area damage and can completely wipe out entire legions of unites in the matter of seconds.

Research for Blasters unlocks at academy level 2

Tier 1: Fitness Training – Increases Blasters health by a flat amount, leads to Silver Blasters
Tier 2: Combat Training – Increases Blaster damage by a flat amount, leads to Ammo Stockpile which increases the ammo held by blasters by 100% while defending garrisons.
Tier 3: Advanced Agility Training – Increases the attack speed of Blasters by x%, leads to expanded ammo capacity which increases ammo held by blasters by 10%
Tier 4: Basic Fitness Training – Increase Blaster health by x%, Leads to Gold Blasters
Tier 5: Convalescence – reduce healing time of Blasters by x%, leads to Garrison Recovery which reduces healing time of garrisoned blasters by 40%
Tier 6: Advanced Fitness Training – Increase Blasters health by x%, leads to Percison Strike which lowers the ammo consumed by the Gold Blaster ability “Fire off” by 30%
Tier 7: Garrison Training – increases the health and damage of blasters while defending the garrison by 20%, leads to Field Training Tundra, which increases health and damage by 20% while fighting on snowy battlefields.
Tier 8: Training Discipline – reduces production costs of Blasters by x% and leads to Brutal efficiency which reduces rare resource cost by 20%
Tier 9: Elite Combat Training – increase blaster damage by x%, leads to weapon research which increases damage by 20%
Tier 10: Advanced Convalescence – more reduced healing time by x%, leads to more garrison recovery for a total of 100% increase garrison troop healing speed.
Tier 11: Elite Agility Training – Increase attack speed of blasters by x%, leads to superior Ammo Capacity which increases the ammo held by blasters by 20%.
Tier 12: Elite Fitness Training – Increase health by x%, leads to Regroup which increases the troop size of blasters by 2