When did Egypt build a professional army?

Answer 1

It was a gradual process, starting after the Hyksos invasion(15th dynasty: 1720 BC). The 16th and 17th dynasty saw Egypt divided. It was reunited in the 18th dynasty when the Hyksos were driven out (1550 BC). After this, a professional army was seen as needed to protect from future invaders. By the 19th dynasty Egypt had a well-trained and professional standing army.