This tech, once acquired, allows an empire to (nearly) permanently assign select military ships to system defense.
This allows you to convert a navy (military) ship by removing the ability to leave the hex- the ship is essentially treated as a national guard unit. The number of harbor ships cannot exceed the CAN of the orbital bases present. Normal CAN limits of a SQ still apply (i.e., the (D17.0) rules apply). These squadrons are exempt from reductions due to CAN-3 (B1.110), CAN-4 (B1.115), and CAN-5 (B1.120). They don't need to pay for this exemption via (B1.130).
Each ship so converted provides a one time income of 20% of the EPV of the ship (assume no surcharges nor discounts). Any number of military ships can be converted in a turn. Reversing the process to make the ship a normal space worthy vessel again can be done at a rate of 2 ships/turn, and it costs 2xEPV. While in harbor guard mode the AF/DF of the units is decreased by 20%.
Examples:
If the system has a single MB in orbit, a single squadron of 6 slots [see (D17.0)]. If it had a SB and a MB, it could have two squadrons- one with 6 slots (controlled by the MB) and a second one with 10 (controlled by the SB).
If the empire had EFO (D17.25), and a MB, it could convert and assign 9xFF to Harbor Guard duty. Assigning 2xCC to the same squadron would be illegal (D17.40)
MB(HBM, 6xFTR, 9xFF)
This tech is only available after a successful R&D program (D1.0). It is available starting in Y100.