USA: Min. of Aircraft Production - Personal Letter Section

Hello All,
on the following item from March 1943 from the US to UK there are two handstamps new to me:
- Circular "Ministry of Aircraft Production - Personal Letter Section"
- "Technical Data / Unlimited License / U-N-103"

Detail:

Could anyone comment on the background of these marks? Are they considered censor marks?
best wishes
Peter
on the following item from March 1943 from the US to UK there are two handstamps new to me:
- Circular "Ministry of Aircraft Production - Personal Letter Section"
- "Technical Data / Unlimited License / U-N-103"
Detail:
Could anyone comment on the background of these marks? Are they considered censor marks?
best wishes
Peter