History Oboe (navigation)

1 history

1.1 background
1.2 initial proposal
1.3 development , testing
1.4 service
1.5 german countermeasures
1.6 late war use

history
background

in order accurately determine location relative objects on ground need 2 data points; 2 angles (as in triangulation), 2 distances, or angle , distance. using radio provide or of these points area of continual development leading start of war. germans pioneered approach operational systems lorenz beam , x-gerät used 2 narrow beam-like signals crossed @ point in sky indicate target. later during blitz, germans introduced y-gerät, combined single lorenz beam transponder-based distance measurement fix locations. problem of these systems produced no information except within narrow beams, , not useful general purpose navigation.

a more useful system introduced in gee system, used 2 timed signals allowed navigator on bomber determine location. used anywhere within line-of-sight of transmitter stations in uk, , provided reasonable signal 500 kilometres (310 mi), depending on aircraft s altitude. gee read on oscilloscope display 3 inches (76 mm) across, limited accuracy of timing measurements. result, gee accurate on order of kilometers, extremely useful navigation , area bombing, did not provide accuracy needed pinpoint bombing.

as accuracy of gee largely due mechanical size of indicator unit, accuracy improved using larger display. however, in these days of cathode ray tube (crt), such displays extremely expensive , long, made them unsuitable fitting large number of bomber command aircraft.

initial proposal

the concept of reversing display arrangement display on ground , transmitter on aircraft obvious. had first been suggested alec reeves of standard telephones , cables in 1940 , formally presented of francis jones in spring of 1941.

the basic idea have 2 ground stations periodically send out signals on similar separate frequencies. aircraft carried transponders, 1 each signal, re-broadcast signals upon reception. timing total round trip time broadcast reception , dividing twice speed of light (the signal travels aircraft , again) distance aircraft determined. identical radar, exception transponder amplified signals return journey, aided accuracy providing strong, sharply defined signal pulses.

a practical problem using these range measurements guide bomber towards target. in case of y-gerät, single beam used produced natural path bomber fly along, , range along path needed measured , relayed bomber crew. in case of system using 2 range measurements, there no inherent path in sky aircraft follow. locations , directions determined 2 range measurements , plotting them on map, doing complex , time consuming, slow provide desired accuracy.

oboe adopted simple solution problem. before mission, path defined represented arc of circle radius passed through target measured 1 of 2 stations. station given name cat . aircraft use conventional navigation techniques, dead reckoning or gee if equipped, place distance north or south of target on point near line. begin flying towards target, @ point operator @ cat call out corrections have aircraft fly closer or further station until flying @ precisely right range.

the cat station continued keep aircraft positioned @ precise distance flew towards target, causing aircraft fly along pre-defined arc. second station, code-named mouse , calculated range target before mission. bomber approached target first call out heads tell bomb aimer begin run, , second signal @ right time drop it. using method there no need 2 stations compare measurements or perform trigonometry determine actual location in space, both performed simple range measurements directly off screen.

in practice, ranges not sent voice aircraft. instead, tone generator produced morse code dots or dashes under control of operators. similar beam systems lorenz, uk aircrew familiar using blind landing aid in pre-war period. if aircraft close station operator play dot signal, , when far, dashes. 2 mixed approached correct range, signal turn steady tone. periodically signal keyed send out letter indicate how far correct range, x indicating 20 miles (32 km), y 10 miles (16 km), , z 5 miles (8.0 km). likewise mouse station sent series of keyed signals indicate approach, s indicate approach starting, , a, b, c , d aircraft approached.

development , testing

the left side of image shows oboe navigation console. 2 crts, of largest built during era, used gross , fine distance measurement. control room built nissen hut (or similar) may suggest 1 of mobile sites moved continental europe after d-day.

there obvious problems approach, however. 1 of obvious given ground station track single aircraft @ time, compared gee bomber pick signals uk , carry out necessary calculations. did not eliminate useful system; y-gerät had same limitation, used target marking. more worrying concern bomber aircraft have fly straight , level along gently curving path while ground operators determined range , radioed corrections. during time aircraft open attack, considered suicidal. , finally, pointed out british had jammed y-gerät, before used, there no reason expect germans wouldn t same detected signals.

despite widespread opposition use of oboe, a.p. rowe ordered development begin. development began both on 1.5 m wavelength shared uk radar systems, @ new fashionable 10 cm microwave wavelength provided cavity magnetron. latter not provide higher accuracy, largely immune jamming unless germans developed own high-power microwave devices, occurred in last days of war.

two stations set far east possible, 1 in dover (walmer) , second in cromer (raf trimingham)). on given mission, 1 of stations cat , other mouse. in testing in september 1941, aircraft flying along arc 130 kilometres (81 mi) dover demonstrated accuracy of 50 metres (160 ft), better bombing method in use. accuracy bombs not quite good, bombs not identical. in demonstration senior officials on 2 july 1942, system demonstrated real-world accuracy of 65 metres (213 ft).

oboe first used in experimental operations short stirling heavy bombers in december 1941, attacking brest. these aircraft had relatively limited service ceiling, , limited attacks @ short-range maintained line-of-sight uk.

at time there great debate taking place in bomber command on use of pathfinders , specialized aircraft , crews find targets , use flares mark them attack. same technique had first been used during blitz germans, notably specialist kampfgeschwader 100, effectiveness had been severely curtailed british jamming efforts. nevertheless, concept had enough backing small force of mosquitoes had been organized operate pathfinder force, using normal optical sighting. proved disappointing in practice, offering slight improvement in accuracy.

but mosquitoes aircraft had performance fly @ altitudes @ oboe signals received on germany. @ meeting in summer of 1942, agreed pathfinder mosquitoes equipped oboe. having faced opposition before, addition of oboe upset argument against specialist role, , become pathfinder force began forming on ongoing objections.

into service

the first experiments oboe in combat setting on germany began on night of 20/21 december 1942, when small force of 6 oboe-equipped mosquitoes sent bomb power station @ lutterade in holland, on german border. 3 of sets failed, 3 remaining aircraft, led squadron leader l.e. bufton, able drop properly. follow-up reconnaissance mission next day showed 9 of bomb craters identified, of them clustered closely 2 kilometres (1.2 mi) away target. similar tests small numbers of oboe aircraft, dropping flares small numbers of avro lancasters following them, made throughout december , january.

at first, germans wrote off these small attacks nuisance raids, intended upset production sending workers air raid shelters. however, realized odd occurring; aircraft dropping 6 10 bombs, through heavy cloud cover, , having 80 90% of them hit targets, blast furnaces or power stations. part of process, bombers released photoflash flares, lit ground below aircraft enough photography. on 7 january 1943, hauptmann alexander dahl noted these , suggested using photographs correct measurement errors of new bombing system.

this precisely had been happening. while oboe demonstrated accuracy on order of tens of meters on uk, on continent tests produced worse results. clear there pattern misses, surmised due differences in surveying grids used on continent. solution problem provided germans themselves; prior war had made effort calibrate 2 systems in series of cross-channel measurements uk ordnance survey received. using these corrections able address inaccuracies immediately.

by late spring bomber command crews had practised bomb-on-marker technique enough begin major operations. harris began series of raids known battle of ruhr, opening raid on essen on 5 march produced rather poor results in spite of proper marking. next major raid against krupp factory in essen on 12/13 march more successful, followed mix of raids met different results. may, however, technique tuned , series of large raids, typically 500 800 bombers, demonstrated increasingly successful results. among these late-may raid on dortmund caused hoesch steelworks cease production, , late july raid on krupps goebbels stated had caused complete stoppage of production in krupps works . analysis of results demonstrated number of bombs fell on targets doubled pre-oboe era.

german countermeasures

oboe missions identifiable german radar operators; aircraft start distance north or south of target , approach on arcing path referred boomerang . although operators became accustomed these aircraft, arranging interception of high-flying , high-speed aircraft proved extremely difficult.

it took germans more year decipher operation of system, in effort led engineer h. widdra, had detected british pip-squeak identification friend or foe [iff] system in 1940. first attempt jam oboe took place @ end of august 1943 during attack on bochumer verein steelworks in essen. system set @ maibaum tracking station in kettwig broadcast false dot , dash signals on 1.5 m band, hoping make impossible pilot figure out if @ right position. same technique british had used against german systems during blitz. however, time oboe system had moved microwave-frequency 10 cm oboe mk. ii, deliberately continued broadcasting older signals ruse.

the failure jam oboe remained mystery until july 1944, when older signal apparently marking 1 target while pathfinder marked another. germans surmised there signal or system being used. time acquainted british microwave systems, in april 1944 raf had introduced oboe mk. iii, resisted german jamming efforts. mk. iii allowed 4 aircraft use single set of frequencies (stations) , allowed different styles of approach, not arc.

late war use

by point battle of ruhr long on , majority of raf s bombing efforts concentrated on targets far germany visible oboe. h2s took on primary role in era. d-day invasions , subsequent breakout allowed addressed setting new oboe stations on continent.

late in war, oboe used assist food drops dutch still trapped under german occupation, part of operation manna. drop points arranged dutch resistance , food canisters dropped within 30 m (98 ft) of aiming point using oboe.