I don't understand this card. The wording appears to contradict each other. For this effect to be true you would need to have no ready defenders. Thus you would focus this enhancement to put into play a ready unit you control.

You don't have any ready units, or you would have used him already.

The text should be changed to: Should you be engaged and have no ready defenders,  focus this enhancement to remove a focus token from one of your units. Put that unit into play as a participating unit in the engagement.

What do you all think? Have I missed something?

Units are only defenders when they are participating in an engagement on your opponent's turn. This lets you bring any ready unit into the engagement from outside the engagement with the action. There is an action window between each strike, so you can bring in the unit with this after all your defending units are focused (from tactics or striking) or destroyed. It also lets you get around some cards like Blockade Runner or Sleuth Scout which prevent you from declaring defenders but not from bringing them in via actions like this one.

oops, you are right there! Next time I should check the affiliation of a card. It still stands that you could use it to circumvent similar restrictions if they exist.

Units are only defenders when they are participating in an engagement on your opponent's turn. This lets you bring any ready unit into the engagement from outside the engagement with the action. There is an action window between each strike, so you can bring in the unit with this after all your defending units are focused (from tactics or striking) or destroyed. It also lets you get around some cards like Blockade Runner or Sleuth Scout which prevent you from declaring defenders but not from bringing them in via actions like this one.

Good catch! I was thinking all ready units were defenders when I would be on the defenseive, and not *ready defenders.*

Is this card working if you have no defenders at all?

Yes, that satisfies the condition.