Why did the raw decrypts of German messages rarely leave Bletchley Park?

The raw decrypts of German messages rarely left Bletchley Park because analysts at the facility needed to process the information first. They sifted through the raw data to prepare intelligence reports that carefully concealed the true source of the information, ensuring that the Allied ability to read enemy communications remained a secret.1

Maintaining this secrecy was a fundamental ethical and strategic priority, as the entire Ultra operation relied on the Germans remaining unaware that their Enigma and Tunny cipher machines had been compromised. By filtering the raw decrypts into actionable intelligence, the British could act on critical information—such as the positions of U-boats—without alerting the enemy to the breach.1