"It may be doubted whether so small a number of men ever employed so short a space of time with greater or more lasting effects upon the history of the world.” — Sir George Otto Trevelyan on the Battles of Trenton and Princeton
Yes, he is referring to the Blockhouses event. My interpretation of the rules is that these "response" cards can only be played as a response to something your opponent is doing.
If it is your turn, you cannot play the blockhouses event to place the blockhouse markers on the board. You would only be able to place the markers if it was the opponents turn and he was about to roll on the raid table.
Am I understanding this correctly?