I actually just did a lot of reading in anticipation of a History podcast I run with a friend a few weeks ago on the Battle of Britain. In the episode I mentioned Bletchley Park by name because yes, they did offer a lot of help to Britain.

Führer Directive No. 16 or On preparations for a landing operation against England was intercepted because Göring transmitted it to the Luftwaffe Air Fleet commanders by coded radio messages. It was then decrypted at Bletchley Park. This had the effect that the British knew (at least in broad terms) exactly what the German's were planning, and most importantly, when.

In addition, during the whole of the Battle of Britain, the Dowding System incorporated Ultra assets into their reports, helping to establish the strength and composition of the Luftwaffe's formations, and the aims of their commanders. An SIS unit was provided at Fighter Command HQ to help sift through the information from Bletchley in order to determine what was essential to parse onto Dowding as well.

It's important to note that it's the entire composition of the Dowding System that helped to spurn the RAF to such success. It wasn't just one piece, be it Ultra, RADAR, the spotters, the skill and will of the people. It was everything put together that provided it's effectiveness.

One story that really stuck to me, about the importance of OPSEC, regarding what was called the Battle of the Beams.

During the Battle of Britain, being able to bomb accurately at night was an incredible asset. This was before (and for the British, during) the invention of Radar, so both attackers and defenders were basically blind. If the attacker could fix their target somehow, they were at a severe strategic advantage.

The Germans developed a targeting system based on radio transmissions. By using two radio towers and constructive interference, they could have a directed radio signal that was only audible along a straight line. German bombers could use the radio signal to stay on the line, and therefore could attack cities with a high degree of accuracy.

Once Britain figured out what was going on, they deployed countermeasures by interfering with the radio transmissions, steering the Germans off-course. This went back-and-forth a few times, with the Germans developing new radio aids and enjoying a few weeks of accurate bombings, and the British reverse-engineering new countermeasures.

So now we get to Bletchley Park: While the Germans were still developing a new guidance system, the British used Enigma to discover it's name. Not any technical details, just the semi-official project name: Wotan. Wotan is the German name for Odin, who among other attributes, only has one eye. Based on this name, British intelligence was able to infer that the new guidance system was a single-beam setup (instead of the previous double-beams ones). This piece of technical insight is what allowed the British to develop effective countermeasures to Wotan, effectively removing Germany's ability to perform effective night raids.

The moral of this story is, always use a random generator to name your secret projects.

Wikipedia link on the Battle of the Beams. British Intelligence in general provided more assistance than just the name in developing targeting countermeasures, but that's one piece of information in particular that they likely would not have any other way of obtaining outside of cracking Enigma.