Though of course the winter weather makes operations most difficult.

They're exactly the sort of people you'd want in any difficult operation.

I presume it will be a difficult operation, otherwise why would he need so many men?

It had compromised their security, made the operation more difficult.

It was a schedule of difficult operations with the statistical results.

They were all difficult operations and needed several hours to accomplish.

After dark, reading or writing was a difficult operation.

Financing the project is likely to be the most difficult operation.

Changing banks is still, in too many cases across Europe, a slow and difficult operation.

Also, he had nearly always asked for some form of plastique while on a difficult operation.