Hello Helen,
First of all, I would like to take this opportunity to welcome you to MLU, and thank you for your support! We are quite unlike any other website in the depth of knowledge and variety of interests held by our membership, and I hope and believe we can help you find the information you seek. Certainly, the sappers on our forum will be able to enlighten you a bit as to the type of activities your father would have been involved with - bridge-building was just one of them.
From here, I'll turn this over to our sappers and historical experts for their input and expertise...
Geoff (aka 'Jif')