The most absorbing thing, however, was the preparations to be made before Colin could be transported with sufficient secrecy to the garden... It was almost as serious and elaborately thought out as the plans of march made by great generals in time of war.

What is the meaning of the figurative language "the plans of march made by great generals in time of war"?

They must be careful and go undetected.

They need a lot of people to help them.

It is a big undertaking.

It took a great deal of strategic planning.