1. Interjections are usually types of slang and considered informal. Often they reflect strong feelings or opinions. They would not look right in a professional style communication.
2. In World War II, German submarines were called U-boats. They sank many Allied transports and freighters. The Allies worked on breaking the U-boat radio code, but they weren’t successful. In 1942, British commandos captured a U-boat. Although it was wrecked and abandoned, the commandos got a German Enigma code machine from it. After the Allies broke the Enigma code, they could locate German U-boats and destroy many of them.