Both no1 and no5 docks were extended in at least two stages.
No1 was initially extended to Rose Brae then at a later date extended to Church St
I thought I posted a thread about this but can't find it and can't find my notes either - doh - senility creeping in.
If anyone's interested and has the time the following search terms help
"Birkenhead Iron Works"
Grayson's graving dock
Clover grayson docks