Pacific Pioneers: the story of the engineers of the New Zealand Expeditionary Force in the Pacific
Chapter Eight — Bridges
In actual operations the bridging work accomplished by the 'Pacific Pioneers' was very different from that which was originally thought probable. The circumstances of 'island hopping' completely altered the whole appreciation of the problem and the geographical conditions encountered called for a change in bridging policy. Limitations on shipping space precluded the carriage of bulky and slowly unloaded bridging equipment which, in any case, could not be transported to the sites until roads were formed. Island water obstacles, usually small in span, were therefore surmounted initially by the construction of fords, replaced early by temporary timber structures and eventually by more elaborate bridges. While such bridging was necessarily slow compared with the erection of standard equipment, the usual lack of roads and tracks meant that speed in bridging was not, at least during the assault phase, a vital factor. So, while roads and tracks were being constructed, the native timber bridges could be simultaneously completed.
In Fiji, since our role was chiefly a defensive one, the preparations made envisaged extensive bridge demolitions, rather than bridge building. Working platforms were therefore the first care of the carpenters and the would-be demolitionists. These were constructed by the 20th Field Company under every sizeable bridge along King's Road, Queen's Road and Prince's Road, on the Suva side, with preparations for the same in other sectors. Under the decking and steel girder spans of Tamavua's composite creation, neat working decks were built and boxing for the charges placed on the girders. This treatment was also accorded page 47the Samambula bridge, the next in size, while holes for the wrecking of abutments were sunk adjacent to the wingwalls. Culverts and embankments came in for their share of the treatment and for many a long mile through many a warm day, the concrete pipes and post hole borers, the jumping bars and camouflet sets prepared the defence areas against the day of the 'last stand.'
Five bridges from Nausori to Mbau, 11 bridges from Nausori to Londoni, another 12 bridges and additional culverts in the peninsula proper, these would have provided us with many a headache if D, for demolitions, day had arrived. We toured around in cheerful lorryloads to argue underneath the arches as to the best means of their disposal. Even on that elegant engineering feat, the Rewa River bridge, we plotted devilishly its overthrow and rather hoped for a quiet chance to practice the laying of gelignite plasters on 'third points 'of the spans. However, in spite of our increased glibness on trusses, stresses and RSJs, we were fated to leave every bridge in Fiji still standing. We even supplemented the existing ones with some new creations of our own: a bush timber bridge produced on the first engineer manoeuvre in Fiji, a 40-foot span bridge in concrete and wood down through the yangona plantations on the Samambula, a 12-foot span timber effort on the Vunda Valley road, on which we gave a hand to the FDF, and also a smaller bridge on the new Momi road. Survey of the bridges in the sectors for their tank carrying capacity was carried out and the strengthening found necessary was in several cases carried out by the 24th Army Troops. The same job, reporting on the strength and carrying capacity of bridges, was our introduction to the bridges of New Caledonia.
The possibility of defence still had to be borne in mind when we arrived in the 'Pearl of the Pacific' The 37th Field Park, it is true, had been formed in New Zealand and was to follow the advanced guard with loads and loads of heavy equipment and bridging gear. But Guadalcanal fighting was still headline news and we were not sure that Necal might not be the same before long. We therefore plotted the 57 bridges running over the burns of the south-western Caledonian coast and at the same time charted tank detours when the bridge appeared delicate. For the most part, however, we found that the type of bridge with which we were to be most concerned was the 'manoeuvre' type. The page 48advent of SBG (small box girder bridging) at Népoui was the signal for various experiments in its use. At Voh we erected a mosquito proof pier in tubular steel (TS) and folding boat equipment (FBE) as well as the SBG, floating bays and decked rafts. A total length of 194 feet would have berthed barges or lighters up to a capacity of 200 tons. At the famous Styx exercise at Pouembout we literally threw the bits of bridge across the stream, aided and abetted by the general, the CRE and a tot of rum. On the Tonta exercise we demonstrated the infinite possibilities of pre-fabrication when it comes to putting up tubular steel trestles. Training by units in the use of SBG. FBE. kapok assault rafts and assault boats was the order of the day for several months, March to June, 1943. We built bridges with FBE. in one case launching SBG from each bank to a boat deck raft and covering a gap of 130 feet. This took us three and a quarter hours in daylight and a mere five hours by moonlight. Assault boat training combined with bridging to give us such hot times as three men a minute for each boat across the same gap. The presence of an enemy artillery barrage would doubtless have halved these times to a record.
Not content with the army issue article we set to work with barbed wire and niaouli and she-oak to make a 100-foot span suspension bridge 20 feet above water level as an access to the Taom River roadhouse and cinema. More substantial access bridges were built by the 23rd Field to Whare puhunga and to the Scots Battalion. It is recorded of one such suspension bridge that 175 man-days were consumed in the task of unwinding barbed wire cables, cutting" it into hangers of suitable length, climbing up she-oaks to affix the cables, swimming across the stream to hitch up the hangers, chopping neat sections of niaouli for the decking, tieing up sacking on a barbed wire section to act as a handrail. Niaouli being a medium hardwood timber and heavy, two fat anchors. 10 feet by 12 inches diameter, rested on the bottom of seven foot holes and successfully carried a heavy traffic. With these bridges successfully achieved and the great thoughts we cherished about exactly where, how and when to build similar ones, we were well equipped to meet the problems of the Solomons campaign. When we remember, too the number of officers and NCOs who went home at this time for bridging courses and combined operations courses, etc. etc., it is apparent page 49that we had, at least, got out of the rut and were going to get a little more ruthless ourselves.
We pass by the Guadalcanal diary to record our monuments on Vella and Mono. In the CRE's intelligence summary the epitaph reads as follows:—
|Name of bridge||Made by||length-width||Man-hours|
|Joroveto-Vella||20th Fd.||110' x 24'||3.900|
|Saveke-Mono||23rd Fd.||115' x 17' 6"||2,900|
|Kolehe-Mono||23rd Fd.||54' -t 1-'||940|
|Boxo Ck.-Mono||23rd Fd.||50' x 12' 6"||650|
|Bryant's Ck.-Mono||33rd Fd.||48' x 15'||1,166|
|Mara Vari-Vella||20th Fd.||45' x 24'||1,914|
|Kolehe Ext.-Mono||23rd Fd.||44' x 12'||1,001|
|Biporo 2-Vella||26th Fd.||36' x 20'||1,070|
|Biporo 1-Vella||26th Fd.||28' x 20'||681|
|Uzamba-Vella||2oth Fd.||25' X 2J'||900|
The above displays of engineer skill, industry ami powers of improvisation show a singular agreement in the unit rates of construction. It is estimated there from that a good sapper working at his usual rate, tropical, can easily build one square fool of bridge in about 1.77 hours.
Almost all of these creations were built on coconut crib piers and decked with coconut logs and coral surfacing. The full description of the Joroveto bridge on vella Lavella is given since the two bridges built at that spot best illustrate the problems attendant upon the use of rough timber and inadequate bridging equipment. The first bridge built here was typical: it was of two spans 30 feet long, resting on a centre crib pier 10 feet long, the length between bank seats therefore being 70 feet. Loose shingle and mud formed a difficult bottom with a high water level of seven feet six inches. The sills, one on each bank, were of local bush timber, mahogany, procured on the site, but the other timber including the stringers was all coconut. There was, as usual, difficulty in obtaining sufficient straight coconuts of a similar size and this was added to by the complete lack of bolts or spikes. The crib, 14 feet by 12 feet base, 14 feet by TO feet top, and nine feet six inches high, had to be lashed in the following manner A half inch steel rope, the heaviest available, was placed completely around the timbers of the crib's high side, the ends of the rope were then spliced together and a pole four inches in diameter and six feet long was inserted in the rope and used to twitch it tight. It nearly parted under the strain but not quite. The crib having been constructed on the left bank of the river, it had to be warped out into midstream position. Skids were page 50therefore dug under it, on the launching side, two winch trucks were placed On the right bank and winch ropes fastened on to the crib. Both winch ropes were passed under the crib, completely over and around it, so that the strain would have a compressing effect on the crib. The two trucks then hauled it into position in less than 30 minutes, the pull being direct and without purchase. The crib was then filled with coral rocks. The stringers consisted of ten coconut trunks to each span. Three from each side were cut long enough to reach right across the crib, thus offsetting its tendency to tip when the load was on one span. All other stringers were given three feet of overhang on each end because of the soft foundations and the consequent possibility of subsidence. The measure proved its worth at a later date when considerable subsidence took place as a result of flood scouring; but the bridge did not part and still carried heavy traffic. Before the flood damage it was proved capable of carrying loads of two heavily laden six-by-six trucks at one time plus a 17 ton D-7 tractor with blade.
The glory of the second Joroveto bridge excelled that of the first by reason of the quality of timber used in its construction and the ingenious devices adopted for pile driving in the absence of proper equipment. Mahogany from beautiful big trees was used for piles and bank seats—logs measured up to 60 feet long and 30 inches diameter. Being near the site they were readily hauled into position. Since, however, there was no pile frame available, attempts were made to sink the piles by combined water and air jetting. This method provided insufficient penetration on the first pier so an improvised piling hammer or monkey weighing approximately 2.000 pounds, was rigged up. A timber guide piece was bolted to the head of the pile and the monkey loosely fastened over it. Control of the monkey during driving was thus ensured. By this means a penetration of up to seven feet six inches was produced into the bed of the stream—a most necessary precaution at a site subject to such heavy flooding. The decking was at first of coconut but was later replaced by sawn timber from the Seabee mill.
In view of the difficulties encountered by the American forces in getting equipment ashore from the LSTs through heavy surf during their operations on Bougainville, a new eventuality had to be provided against in the proposed Nissan operation. It was page 51considered essential by the US authorities to have on each TST American trestle bridging equipment with a crew trained in its rapid erection. This would facilitate the rapid unloading of these vessels. So in late January of 1944 a special week of training was put in by 20th and 26th at Tulagi. When D-day came, however, it proved happily unnecessary to attempt to break our established 50 minute record. The gap, which it was feared might exist between the LST ramps and the shore did not appear. To the loud cheers of the sappers, hanging eagerly over the bows with their fingers crossed, the boats beached right in. We appreciated the absence of bridging requirements almost as much as the absence of opposition.
Meanwhile the unwanted Bailey bridge equipment, the small box girder bridge etcetera remained with the field park at Guadalcanal to be spat upon and polished, repaired and maintained, ready for instant use. Except on the one occasion when five bridges were swept away there in one night's flooding there was never much likelihood of its being used. On that occasion the US authorities thought that it might come in handy but later changed their minds. A fitting postscript therefore to our bridging operations is provided by that same neglected small box girder adorning the Baraoua stream, an ingenious bond between the four field companies returned from the field and the works company who had remained with the stuff, between the new officers' mess with its parsonical murals, and the Le Glere's farm YMCA. New Caledonia.
'Last scene of all which ends this strange eventful history/ November, 1944, is the Bailey bridge, in all its glory, erected at the foot of Queen Street. Auckland, bv a remnant of 3 Div Engineers, to make a victory loan holiday for a tankload of pretty girls.