Originally Posted by
Easy Street
That's certainly how LRMTS worked on Jag and Tornado: as a means of cueing unguided weapons and providing an accurate range for the trigonometric calculations which generated HUD aiming symbology. The laser transmitter (designed for use at short range when directly overflying the target) was less powerful than those found in targeting pods and ground target markers, but the receiver (designed to detect faint off-board laser signals anywhere in its field of view) was much more sensitive than the "disposable" one found in Paveway guidance heads. So, as the name suggests, LRMTS was suitable for range measurement and detection of off-board targeting laser spots, but not for guiding LGBs.
Why? To aim the LRMTS at a target it was necessary to keep it in the HUD. For designating LGBs this would entail flying well behind the releasing aircraft to avoid being caught in the explosion (bearing in mind that you would quickly catch up with a LGB as it slowed down during the lofted profile) and this would mean an increased range between laser and target, compounding the effect of the low power and making the reflected signal too weak for the LGB to detect. The geometry of the target matters too; lofted LGBs come in quite flat so the laser really needs to be shining onto a vertical surface to give optimum reflectivity. That is sometimes hard to achieve with a modern targeting pod, let alone through a HUD at long range!
The document link below covers the employment of LGB's in some detail. If the LRMTS can't produce a PRF code that the Bomb can recognize. it wouldn't guide even if it could detect the reflected light (unless there was a "Guide on any L@ser light you can see" function on the guidance unit switches) and of course that the Wavelength of the IR light being produced by the L@ser ranger and the IR bandwidth of the Seeker in the bomb overlap. Jerry Pook's book covers the problems with employment of the Paveway II in the Falklands war and the main issues that stopped the weapon from being successful until the last day of the war were more a case of Duff Gen (the fact that somebody had told the 1(F) crews that LRMTS could guide a Paveway) and Duff Batteries (in the ground based designators) on the first attempts to use the weapon. I can't find my copy of Pook's book, but the first attempted mission with LGB's was on 30th May 82
https://fas.org/man/dod-101/sys/smart/jp3_09_1.pdf
https://fas.org/man/dod-101/sys/smart/jp3_09_1.pdf