Bombard

Military Academy: Increase the production speed of infantry, cavalry, siege, and transport units at buildings by 33%. Does not affect religious units or other support units.

Chemistry: Advancements in alchemical research increase the bonus damage of all gunpowder siege weapons by +25%.

Siege Works: New carpentry techniques increase the health of siege units by +20%.

Siege Works (Improved): New carpentry techniques increase the health of siege engines by +30%. If Siege Works has already been researched, increase their health by +10% instead.

Greased Axles: Increase the movement speed of siege engines by +15%.

Greased Axles (Improved): Increase the movement speed of siege engines by +25%. If Greased Axles has already been researched, increase it by +10% instead.