[Milsurplus] F 1528 SR/ 16-30MHz filter, what is it?

[boeing377 at aol.com]

  Bought a beautifully made dual section tunable 16-30MHz "band 
suppression filter" at a ham swap. It runs on 15 VDC and is part of 
Filter Assembly FS 1523/SR, made for Space and Naval Warfare Systems 
Command by Cincinnati Electronics. What is this, an HF notch filter? 
What active ckts are in the powered cans? Has two front panel dials 
each with markings from 16-30 MHZ and a toggle with two positions, IN 
and FILTER.