Low Altitude Bombing System Tests
The Official Report - November 1955
by then Capt. John Harris
The following is an exact copy of the draft final report. This report has lain in my dresser drawer for more than forty years.
THE NOTES, (Accompanied by spotting towers target markings)
Brackets [ ]indicate editors notations.
Arrived Wheelus [Air Base] 25 November 1955 in B57-B #52-1564 for the purpose of making preliminary drops by LABS method with three pound practice bomb from T-1 rack. Aircraft was not equipped with any LABS gyro or computer. Drops were to be made in accordance with material furnished by Eglin [AFB], or any method found to be more suitable. Contacts were made with OIC [Officer in Charge] Special Weapons 48th Fighter Bomber Wing who were TDY [temporary duty] at Wheelus at this time. Valuable information was volunteered by this organization. It was their opinion that an extreme low level approach was more suitable than the 1000 ft. approach recommended by Eglin, however no computer and no bombing tables were available to us for this mission. There was no optimism evident from them as to the outcome of this experimental project. It was decided that two possible choices were open to us. First, to drop from 1000 ft. absolute altitude using the gun sight depressed to 5.7 degrees to establish pull up point and release point determined by attitude gyro tumble, as per Eglin report. Second, to use time and distance measurement with a stop-watch from an initial point a known distance from the target. The approach to target to be made at extreme low level.
On the 27th of November, a dry run mission was flown over the Tarhuna LABS target for orientation and practice approaches using Eglin method. Altimeter error was found to be negligible at 420 knots 1500 ft above sea level when measured with S-4 SHORAN [Short Range Navigation] equipment over the ocean. However, later it was decided that considerable altimeter error did exist (300-500 ft) when figures were checked as to pull-up distances from target.
The first live mission was flown 28 November . Eight drops were affected using the Eglin system. The first three drops were made with no wind correction applied, and hits were 2500, 2300, and 1800 ft long at 12 o'clock. The first indication of gyro tumble was used as release point. In an effort to bring bombs onto target, pilot applied correction to release point, that is, 135 degrees of precession or tumble instead of the first indication of tumble. The next bombs were scored at 700 ft. 9 o'clock, 1150' at 7 o'clock , 1200 at 05:30 o'clock, 900 at 07:30 o'clock, and a SHACK [bulls eye]. Indicated air speed was approximately 425 knots and g's recorded in pull-up at 3.5., indicated altitude averaged 1520 plus or minus 20 ft. Target elevation was 504 ft. Average distance short of target for pull-up 4450 ft. as measured by stopwatch from IP 13,194 ft. from target. Actual time of fall of bomb release to impact, was found to be 38 seconds. Time from start of pull-up to impact was found to be 51 seconds. No check was made on escape distance.
This system was found to give satisfactory results. However, considerable difficulty was encountered trying to maintain altitude, air speed, and track exactly for desired results. [The] Eglin report called for 98% power to be applied a few seconds before pull-up causing [the] pilot to neglect flight instruments at a very critical time during the approach. Mathematical calculations showed that any error in altitude or attitude induced large errors in range. (Altitude error gives incorrect distance from target and attitude error of pitch gives incorrect errors in angles of deflection and incidence, thus another error in range (navigator talk)). It is anticipated that rough air would cause even greater errors.
The next mission was flown two hours later the same day. Time-distance measurement with a stop watch from a known point was used to determine pull-up point of 4590 feet short of target. A high speed pass was made from IP [Initial Point] to target (13,194 ft) at 425 IAS [indicated airspeed] to determine ground speed. Stop watch time was 18.8 sec. Ground speed 416 knots or 701.6 feet per sec. It was computed that twelve seconds from IP established the pull-up point, later figured to be 4590 ft. from target. The first bomb was dropped considerably short due to a four second error in timing. The next scores [in feet and clock position]were as follows: 600-10:30, 700 at 8:00, 425 at 9:00, 825 at 5:00, 475 at 8:30, 900 at 6:30. Indicated true altitude for runs was 900 feet plus or minus 50 ft. Actual altitude was 50-100 feet AGL [above ground level] as observed by [the] pilot and range control officers. Altitude at time of release was 5200' indicated and over the top at 6000 ft. Actual time of fall was 37.5 sec. Time from pull-up to impact was 51 seconds. One escape was practiced in full and escape distance was over 3 1/2 miles and range officer stated that the aircraft was out of sight to him at time of impact.
It was determined from hits observed that proper pull-up point should be 4590 feet from target. Later after some 200 drops by the wing, this figure proved to be very near to correct.
It appeared that the altimeter read about 300 feet too high on the aircraft. Power was stabilized at 98% about 3 sec. before pull-up as per the Eglin report. The release point was determined as before at 135 degrees of tumble of the attitude indicator.
Minor variations of altitude and attitude did not appear to be critical in this and later flights where time was used to for distance measurement.
Two other missions were flown the following day expending 13 more bombs for a greatly improved average C.E. [circular error]of 607 feet. The same system was used with one major exception. Power was advanced to 100% (to the stops) about three seconds prior to pull-up. No effect was noticed on hits. This took less time and effort and pilot was not distracted as much at this critical time. The gun sight was used for azimuth control, depressed to 3 degrees. Time from I.P. to pull-up was worked out to the nearest tenth of a second. A.T.F. [actual time of fall] averaged 37.6 seconds. Wind corrections were guessed for the last 13 drops, but a reasonably accurate system using forecast winds was developed. Speed runs from I.P. to target were made at the beginning of each mission, however this would not be necessary since forecast winds would be close enough to compute approach velocity.
It has been established that the aircraft has passed vertical, or at about 100 degrees, at time of release. Delayed releases (in pitch rotation) caused bombs to land short. Early releases hit long.
The minimum altitude approach using a timed pull-up point comparable to system used by LABS computer was favored. It was felt that this would be more practical for obvious reasons of aircraft and crew safety over enemy territory. (End of report)
I found in my dresser drawer, folded together with the hand written notes, two sheets showing the spotting pattern from the towers, along with notations of bomb scores. One shows 6 bombs for an average of 512 feet, and the other shows seven bombs for an average of 710 feet. I think these are the scores for the last two test missions flown on the 29 November 1955.
For the career oriented flying officer, this should have been good "meat" for the upcoming OER [Officer Efficiency Report]. It wasn't mentioned in mine. About two years later, in the squadron commanders endorsement, he commented that I had "greatly enhanced the ability of the wing to complete it's wartime mission, in testing and establishing bombing techniques." I can't remember if I gave Miserocchi appropriate credit, but I hope I did. Anyway, it was a lot of fun!
Note: All the bombing information and calculations came from Lt. Miserocchi. He seemed to remember everything they taught him at Mather AFB. Without his able assistance, the tests would have been far less professional. Much more would have been guesswork. He and one other officer were the only ones to bother checking out a stop watch from supply before departing the States. Everyone else kidded him about it. We couldnt have done the job without it. The two stop watches were hurriedly carried from one aircraft as it landed, to one waiting for takeoff, so every flight had a stop watch!
Lt. Col. Louis F. Miserrochi eventually retired from the Air Force and settled in Austin, Texas. He died of liver cancer in April 1994.