The Civilopedia states that Drill I is NOT available for Melee Units but it also states that Drill II is available and Drill I is required for Drill II. Maybe i have the wrong logic but it seems to me that Drill II can't be reached because of this caveat. 
Edit: Okay i found out that the Samurai (Japan UU ) starts with Drill I thus is the only Melee Unit that can reach Drill II. Is that right or am i daydreaming?
Erebos

Edit: Okay i found out that the Samurai (Japan UU ) starts with Drill I thus is the only Melee Unit that can reach Drill II. Is that right or am i daydreaming?
Erebos