28 June 2012

The Genesis of the B-25 Mitchell Strafer-Bomber

The first strafer package installed on a B-25 Mitchell.
The first half of 1942 in the Pacific were dark days for the Allies. With the loss of the Philippines and the Dutch East Indies and the fall of Singapore in February, Allied forces fell back in the face of the Japanese, seeking refuge in Australia to regroup for the offensive. Australia would soon become the base of operations for General Douglas MacArthur's South Pacific offensive as war materiel from the United States along with personnel began to flow in via a logistical supply line stretching from California via Hawaii and Fiji. It was via this route that the first North American B-25 Mitchell medium bombers began to arrive in Australia- rather unusually, though, the first B-25s to arrive were earmarked for the Dutch and were accompanied by Jack Fox, North American's field service representative. With ten brand-new B-25s present, it wasn't long before some back room dealings resulted in the B-25s along with Jack Fox being transferred to the US Army Air Forces at their new base in Charters Towers which was built in only six weeks by the Australians. Arriving at Charters Towers, Fox saw "his" B-25s arriving with American crews which was unusual as few pilots had been checked out in the new bomber. Fox queried one of the arriving pilots who gruffly responded "Who needs checking out? The damn thing has a stick and throttle, doesn't it?"

That was the legendary Captain Paul "Pappy" Gunn that Fox had just met. A retired Navy flight instructor, Gunn was living in the Philippines working for Philippine Air Lines when the Japanese invaded. Managing to assist the ultimately futile battle against the Japanese, Gunn managed to fall back to Australia where his intimate knowledge of the Philippines was put to use with an immediate commission in the USAAF. Gunn's initial meeting with Fox would be the start of the development of some of the most lethal aircraft fielded against Japanese forces in the South Pacific, the "strafer-bombers". But before we move on, we have to back track a little bit to January 1942 and back to the United States when the tactics of a minimum altitude bombing attack on ships and troops were being discussed within the USAAF. Soon tests were underway at Eglin Army Air Field in the Florida panhandle to develop the technique. By this time the USAAF in the South Pacific under General George Kenney, head of the Thirteenth Air Force, recognized the low-level attack virtues of the Douglas A-20 Havoc and North American B-25 Mitchells, roles they were not originally designed to perform. But Kenney was dissatisfied with the armament and bombs of the two attack aircraft as they weren't completely suited to how he wanted to employ them. 

With flight tests at Eglin AAF and with Kenney's own aircraft in Australia, skip bombing was developed which involved a low level approach against the heavy defensive fire of the Japanese ships. Lacking proper American fuses to perform skip bombing, Kenney had Australian fuses which were longer substituted on the bombs. With A-20 and B-25 crews training locally on skip bombing, the first attacks were found to be more successful if combined with Australian Beaufighters which strafed the ships to kept the defensive fire to a minimum. It was at this juncture that Pappy Gunn enters the picture. He had come up with a field modification for the A-20 that put a battery of four fifty-caliber guns in the nose since a bombardier wasn't needed on low level attack runs. This way skip bombing and strafing could be combined in a single aircraft. The results were better, but extra fuel tanks had to be installed in the Havoc's bomb bay to increase its range, which in turn reduced its bomb load. By by the summer of 1942 A-20s were in short supply as A-20 deliveries to the Russians were increasing.

"Pappy's Folly" with Pappy Gunn at the helm.
And that's when the B-25 entered the picture. It had longer "legs" than the Havoc and could carry a heavier load. Early skip bombing missions had already shown the B-25 eminently suitable for the role. Gunn and Fox come up with a field modification with General Kenney's blessing that put four fifty-caliber guns in the nose section with plenty of ammunition as well as an additional two pairs of fifty-caliber guns on external blisters on each side of the forward fuselage. By the summer 1942 Jack Fox issued a memo to all the other North American field reps in the South Pacific on how to modify the B-25 into a strafer-bomber. North American dispatched an engineering team to the field depot which was located at Eagle Farms in Brisbane to further assist Pappy Gunn and Jack Fox in their development work. The first B-25 Mitchell modified as a strafer-bomber was aptly named "Pappy's Folly" and personally flight tested by Gunn himself as well as Jack Fox. Working out the bugs, General Kenney then sent the two men and "Pappy's Folly" up to Port Moresby closer to the front lines for more testing. By February 1943 the North American team at Eagle Farms converted twelve more B-25s which were then assigned to crews with the 90th Bombardment Squadron in Port Moresby. Tactics were worked out and crews trained on a wrecked ship off the coast of Port Moresby- a pair of B-25s would approach enemy ships at 1,000-1,500 feet and then drop to 500 feet or lower on the final run in to the target. One Mitchell would open up with its gun battery to suppress the defensive fire while the other Mitchell would drop a string of three 250-lb bombs in a skip bomb attack. After the first pass, the pair returned for a second run, this time switching roles. 

During the first half of 1943 General Kenney's "commerce destroyers" wreaked havoc on Japanese shipping in the Bismarck Sea that supported the Imperial war machine. Soon airfields also came under attack by the strafer-bombers dropping 23-lb fragmentation bombs slowed by parachutes- "parafrag" bombs. They would soon be a decisive force in the campaign in the Southwest Pacific on the road back to the Philippines. 

Source/Photos: B-25 Mitchell: The Magnificent Medium by Norm L. Avery.  Phalanx Publishing, 1992, p95-103.

26 June 2012

How Jack Steiner and Joe Sutter Defined the Boeing 737 Configuration

The Boeing 737-100 prototype
Reading aviation history books is one thing but to read about aviation history from one of the view point of someone who played a vital role can sometimes be more enjoyable. One of those books is Joe Sutter's book 747: Creating the World's First Jumbo Jet and Other Adventures from a Life in Aviation from Smithsonian Books. Long employed by Boeing, Sutter led the team of engineers that developed the Boeing 747. But before the 747 came along, Sutter was tapped by his boss, Jack Steiner, to assist with the development of the Boeing 737. The 707 was well on to insuring its place in aviation history and Steiner was flush with success with the creation and introduction of the Boeing 727. It was Steiner who realized that Boeing could create a family of airliners across sizes that could span different market segments in the growing airline industry. By 1964 many of Boeing's competitors were well ahead in the short-haul jet market with the Sud Aviation Caravelle in France having been in service since 1959, the BAC One-Eleven was in flight test in the UK and Boeing's main US rival Douglas was two years head on the development of the DC-9. At a heated and divisive 1964 meeting, half of those present wanted to proceed with the 737 and the other half felt that Boeing's energies were better focused elsewhere given the state of progress of the competition in the short haul market. According to Sutter, the decision was deferred and Jack Steiner was told to keep refining the concept in the interim. 

But that wasn't enough to Steiner. He felt that Boeing should build the 737 and he went around Boeing CEO Bill Allen and personally lobbied each of the members of the corporate board of directors. Bill Allen supported the 737 project but Steiner's determination to get the 737 built didn't win him any points with Bill Allen. But the 737 project was given the go-ahead for launch in 1965. But getting a refined project to launch wasn't easy. Conventional wisdom pointed to a rear-engined T-tail design with five abreast seating which was what the competition used as their respective configurations (though to be fair, the Caravelle's tailplane was mounted halfway down the vertical fin). With Joe Sutter assisting him, the 737's initial designs had a very similar layout. But Steiner's ideas of a family of Boeing jetliners led to divergence- the first of which was the fuselage cross-section. By using a 707 fuselage cross section, they could cut development time, but give airlines six-abreast seating which offered more capacity and operating efficiencies not possible with similarly-sized aircraft with five-abreast seating. 

But going with the 707's fuselage cross section and nose meant the 737 got a bit portly in shape and this led Steiner and Sutter to abandon rear-mounted engines for the 737. Because of the short wide fuselage, aft mounted engines would have to mounted further way from the fuselage to allow for smooth airflow into the planned Pratt and Whitney JT8D engines. This resulted in the need for more structure and more weight, which ended up offsetting the efficiencies of six-abreast seating. Sutter recalled in his book taking drawings of the 737 up to his office and cutting the engines out with scissors and moving them around to see if there was a better place for them. The most obvious alternative to Sutter was to mount them on the wings, but to use a 707-style engine pylon meant that the 737 would need a tall landing gear to sit higher off the ground. Sutter's dealing with airlines indicated that ease of loading/unloading and servicing meant that having the 737 low to the ground would be a major selling point for the planned short haul market. Having the jet lower to ground meant it could be loaded, unloaded, and serviced faster without specialized vehicles, platforms or even ladders for engine work. 

Sutter was stumped. Aft mounted engines were out. Pylon mounted wing engines were out. It donned on him there was a third solution as he moved the engine drawing cut outs around on his desk. Why not snuggle up the engines right under the wings? The key concern was safety and this was solved by putting the hot section of the JT8D behind the aft spar of the wings which meant it was behind the main wing fuel tanks in the event of an uncontained turbine failure. Sutter recalled presenting his solution to the intrigued Steiner, so they decided to do a paper "fly off"- Steiner and an assistant would work up a series of numbers on the performance and costs of a rear-mounted 737 design as the "Red Team" and Sutter and an assistant did the same with his 737 configuration as the "Blue Team". Although they gave themselves two months for the study, the answer was obvious after two weeks- mounting the JT8Ds right under the wings meant six more passengers could be carried for the given configuration. With six-abreast seating, this meant Sutter's configuration for the 737 was the clear choice and the design was locked in late 1964 in preparation for the eventual go-ahead given a few months later by the Boeing board and CEO Bill Allen. This was the design Steiner passionately believed in so much that he was willing do end runs around Bill Allen!

Both Jack Steiner and Joe Sutter shared the patent for the layout of the 737 and the design has gone on to be not just the best-selling jetliner in Boeing's product line, but as the most-produced jet airliner in history- as of April of this year, 7,147 Boeing 737s have rolled off the Renton, Washington, production line since 1967 when the prototype 737-100 rolled out.

More pictures that show the unique engine mounting of the Boeing 737-100/200 family:

On Flickr someone has posted an NAC 737-200 undergoing maintenance with an interesting shot of a "naked" JT8D still mounted on the wing. 

On JetPhotos there is a similar shot of a Malev 737-200's JT8D engine.

Source: 747: Creating the World's First Jumbo Jet and Other Adventures from a Life in Aviation by Joe Sutter with Jay Spenser. Smithsonian Books, 2006, p74-79.

25 June 2012

The Luftwaffe Seenotdienst: The First Air Rescue Units

Cover of a German history book on the Seenotdienst.

Since the beginnings of military aviation air rescue operations had taken place, but the operations were quite ad hoc and improvised in most situations. That would change with the rise of the Luftwaffe which would be publicly acknowledged for the first time by Hermann Goering in 1935. As the Luftwaffe needed to expand rapidly as part of Germany's expansionist aims, the air arm could ill afford the loss of a highly trained pilot or flight crew member. Given that most of the Luftwaffe's taskings were in support of the Wehrmacht, it was expected that most crewmen would bail out over land. Despite this, the Luftwaffe did have a small number of seaplanes at bases in Baltic Sea and North Sea, both of which complicated the bail out from an aircraft in trouble. In 1935, Lt. Colonel Konrad Goltz, a supply officer based in Kiel, was tasked with organizing a system for recovering downed aircrew from the inhospitable waters of the surrounding seas. His initial command consisted of a flotilla of second-hand, if not run-down, boats with local commanders given authority to seek assistance from Kriegsmarine aircraft and local German lifeboat rescue societies. By the following year his units were designated the Ships and Boats Group- an unusual situation of a Luftwaffe officer commanding a fleet of ships!

By 1938 it was apparent to Luftwaffe planners that war with Great Britain was on the horizon and that Luftwaffe crews would be routinely traversing the English Channel and North Sea to strike British targets. In the following year the Ships and Boats Group acquired twelve old Heinkel He 59 float planes which were painted white with Red Cross markings. The aircraft were modified with a floor hatch and extendable ladders as well as a hoist to help lift injured crews into the aircraft. Medical gear, respirators and electrically-heated sleeping bags were also fitted to the old biplane aircraft. Renamed the Seenotdienst (Air-Sea Rescue Service), the Heinkels went into action on 18 December 1939 not to rescue Luftwaffe crews, but downed RAF crews from a Vickers Wellington force that was badly mauled after a bombing attack on the port of Wilhemshaven.

The Seenotdienst's first aircraft, the Heinkel He 59.
As the Reich conquered the Low Countries and Denmark and Norway, Seenodienst units were established in those countries for the rescue of downed aircrews. With the fall of France in 1940, captured French aircraft were added to the Seenotdienst fleet along with larger and more capable Dornier Do 24 flying boats. With the massing of Luftwaffe units in France for the anticipated invasion of Britain, German fighter ace and commander Adolf Galland stressed the importance of water survival to his flight crews- even single seat fighters were equipped with a survival raft and Luftwaffe crews were trained to ditch their aircraft and use the rafts as opposed to RAF crews who were trained to bail out and rely on their life vests. In addition, Luftwaffe general Ernst Udet had a series of rescue buoys placed throughout the English Channel- the buoys could hold four men and were stocked with blankets, dry clothes, food, water, and flares. Painted bright yellow and nicknamed "Lobster Pots" by the RAF, through the Battle of Britain both British and German patrol boats would check on the buoys and unusually, kept them stocked as they knew the buoys could save any downed aircrew regardless if they were British or German. The Luftwaffe also pioneered the use of fluorescein green dye to stain the waters around downed aircrew so as to make their positions more visible to rescue aircraft. The Luftwaffe Seenotdienst also pioneered the idea of a rescue task force with Messerschmitt Bf 110 twin engine fighters assigned the task of escorting and protecting the Seenotdienst aircraft.

Between February and August of 1941, of the over 1200 air crews from both sides that went down in the North Sea and English Channel, 444 of them were saved by the Seenotdienst. Of those 444, 78 were RAF crews. With painful awareness that British efforts were severely lacking in air-sea rescue during the Battle of Britain, in 1941 the RAF Coastal Command set about improving its air rescue capability and would use the Seenotdienst as a model. With the expansion of the US Army Air Forces in Britain, the RAF Coastal Command in turn assisted the United States in developing its air sea rescue capabilities.

Source: Search and Rescue in Southeast Asia by Earl H. Tilford, Jr. Center for Air Force History, 1992, p3-6.