Nuclear Submarine Variants

Question

It's been announced that Australia will now get three in service Block 4 Virginia Class submarines, rather than two in service Block 4 and one new Block 7. This change has been explained as being a better solution because they will all be the same, meaning the Navy avoids having to operate an 'orphan' and it will reduce cost. 1. What is the cost variance the Submarine Agency had calculated between the Navy operating a combination of two Block 4 and one Block 7 Virginia Class submarines compared to operating three Block 4 platforms? 2. What weight does the preference on operating Virginia Class platforms of the same Block configuration carry in deciding to acquire additional Virginia class submarines from the US? 3. How many Virginia Class block variants have Australian naval personnel been trained on in the US? 4. How many Virginia Class block variants are Australian naval personnel undergoing sea service on with the US Navy? 5. What difficulty have Australian navy personnel faced by undertaking training one Block variant and undertaking sea service in a different Black variant?