Complex sentence: Two other Dutchmen followed Steinmetzs actions, one Major Giebel and a Lieutenant by the name of Drjiber used that same way later but the method was discovered on the third try when two more dutch officers tried to get into the man hole they were discoverd by guards.
Split into simpler sentences: Two other Dutchmen followed Steinmetz's actions; one Major Giebel and a Lieutenant by the name of Drjiber used the same escape route. The method was discovered on the third attempt when two more dutch officers tried to use it and were discovered by guards.