A British force of approximately four thousand - which would have been insufficient against a genuine invasion by the army Spain had gathered - was assembled at Tilbury, in Essex, near the Thames estuary.

The gathering is mostly notable for Elizabeth's speech to the troops which contained the line "I know I have the body of a weak, feeble woman; but I have the heart and stomach of a king, and of a king of England too" which is one of Elizabeth's most famous quotes.

This is all very stirring, except it took place about eleven days after the Battle of Gravelines, which was the decisive naval engagement of the armada. It's suspected that Elizabeth was being a canny politician by not letting a good crisis go to waste.

source: The "In our time" bbc history podcast just covered this. I don't know if it's available overseas but it's available here