Originally Posted by Jane-DoH
What kind of tooling do they require that is not required for traditional aircraft fabrication? Is it hard stuff for an aircraft manufacturer to procure in those days?
There is a reference to this in wiki under Barnes Wallis. Tooling in this context would include assembly jigs, generally made in-house to meet the needs of any design. It is part of the cost and time-scale of any project, you don't just build the product, you have to produce the tools and the jigs to hold things as they are assembled.
The Wellington took a lot of (wo)man-hours to build, you can see the complexity in this pic: