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Aerology and Amphibious Warfare

Amphibious Landings in Lingayen Gulf

NAVAER 50-30T-9



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CHIEF OF NAVAL OPERATIONS
AEROLOGY SECTION
WASHINGTON, D.C.

JULY, 1945



Foreword

This is one of a series of pamphlets dealing with the weather aspects of Naval and Amphibious Warfare. The data on which these studies are based are taken from official documents and reports submitted to the Navy Department. The material has been collated and presented in a semi-technical form with particular attention given to the operational aspects of weather.

During the preparation of this study, it was found that weather data submitted by the various commands were occasionally at variance. An effort has been made to reconcile these differences in order to provide an accurate account of the sequence of weather conditions as forecast for the Force Commander, to describe the actual weather conditions observed during the operation, and to give a practical explanation of these weather conditions.

It is hoped that these studies will afford a clear view of the use of weather information during the planning, strategical, and tactical phases of the operation, and that they will form a basis for a better understanding of the application of weather information in future operations.

The primary objective of these analyses is to assist those officers who are charged with the responsibility for the planning and execution of similar operations.

/s/
Vice Admiral, U.S.N.,
Deputy Chief of Naval Operations, (Air).

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Amphibious Landings in Lingayen Gulf

THE SIGNIFICANCE OF WEATHER IN THESE OPERATIONS, AS NOTED IN A REVIEW OF ACTION REPORTS:

BY COMMANDER THIRD AMPHIBIOUS FORCE:

1. In deciding on the route to be followed the Aerological Officer's recommendation was solicited.

2. The expected excellent weather prevailed on S-day.

3. The enemy took advantage of the good flying weather to launch his first attack.

4. By mid-morning of S plus 1 the 6 to 8 foot surf at the beaches resulting from the increased swell had caused landing operations to come to a halt.

BY COMMANDER SEVENTH AMPHIBIOUS GROUP:

1. The Lingayen Area is noted for its high swell, caused by the prevailing strong northerlies off Asia from the Northeast Monsoon.

2. Smoke conditions were good with a surface inversion prevailing at sunrise and sunset.

BY COMMANDER CARRIER TASK FORCE 38:

1. The Lingayen landings point the problem. Here thousands of men moving hundreds of miles in hundreds of ships were dependent for their success on the Fast Carriers gaining control of the air in Northern Luzon and Formosa by a date which had been set weeks before.

2. Actually the weather conditions between S minus 6 day and S day were so poor that the success of our mission was in question much of the time. The above is given to emphasize the necessity of having knowledge of future and immediate weather conditions as accurately as is humanly possible.

3. In addition to the collection and dissemination of data at the fleet weather central it is essential that there be a highly qualified aerologist in the fleet or force flagship with sufficient equipment to permit him to interpret properly local conditions as influenced by the broad weather picture published by the weather central ashore.

4. To date the information available to the fleet has not been sufficient. Whether the fleet borne aerologists are competent to do their part is not indicated because they have not had the necessary knowledge of the general situation. The importance of having the best man available for the job in the fleet cannot be overemphasized.

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BY COMMANDER OF AIR SUPPORT TASK UNIT:

1. Due to the heavy seas, air operations in the objective area were extremely difficult. Occasionally green water was taken over the bows.

2. All CVE's experienced shortage of aircraft, damaged not only in barrier crashes, but also in rough landings under the hazardous landing conditions that prevailed almost throughout the entire direct support period. It is believed that any worse sea conditions would have made CVE operations impossible.

BY A CVE COMMANDING OFFICER:

1. "At sea, however, strong winds, rough seas, and heavy swells were recorded on 6 January and 9 January through 17 January. These conditions definitely hampered landing of planes and the work of the deck crews."

2. The northeasterly monsoon which blows from October to March brings strongest winds of the year to the East China Sea, Formosa, Northern Philippines and the South China Sea areas.

INTRODUCTION

The series of successful invasions into the Japanese-held Philippines which once again placed our forces in control of Leyte, Samar, and Mindoro Islands was the prelude to regaining control of Central and Southern Luzon, the greatest strategic prize in the Philippine Archipelago. Constant pounding of enemy forces in this area by both land-based and carrier-based planes had been in progress for months and had resulted in almost complete demolition of Japanese supply and communication facilities. Our dominance of the air was unquestioned.

Finally, on 9 January 1945, American forces returned to Luzon in strength, landing on the shore of Lingayen Gulf in the same spot used by the Japanese in their landings slightly more than three years earlier. Another great stride had been taken on the Road to Tokyo.

WEATHER PLANNING

Since the decision to invade Luzon was based on over-all strategy, it was necessary to proceed without regard for the most advantageous season from a weather standpoint. Fortunately, however, a relatively dry season prevailed at the time and comparative freedom from heavy swells and surf could reasonably be expected on the leeward side of Luzon.

As in the past, the weather planning phase of the operation was concerned primarily with two comprehensive weather considerations directly related to the potential success of landings on "Sugar Day", specified as 9 January 1945.

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These important factors were:

1. Expected weather throughout the operation.

2. Considerations of a strategic and tactical nature based on the possible effects of weather on the various phases of the operation.

WEATHER EXPECTED

PLANNING STAGE

At a conference of the planning staffs of COMMANDER THIRD AMPHIBIOUS FORCE and COMMANDER SEVENTH AMPHIBIOUS FORCE, the problems associated with and resulting from the various weather phenomena of the prospective area of operations were discussed and the necessary plans made.

In formulating the weather plans the first step was to consult all available publications concerning normal conditions enroute to and in the Philippine area during January, with particular attention to Central Luzon in the first and second weeks of that month.

Decision as to which of two suggested routes to be followed to the target would be most advantageous considered as a factor the relative protection against typhoon and cyclonic activity afforded by each. The probability of such activity, while not as great a potential danger as in some previous landing operations, still could not be disregarded.

TYPHOONS

While the Philippines have been affected by typhoons in all months of the year, the minimum number occurring in February and March, the month of January is relatively free of such phenomena. Furthermore, the mean typhoon track at that time is across the southernmost islands of the Philippine group and thence westward, with the typhoon frequently dissipating in the western area of the South China. Sea.

NORTHEAST MONSOON

From November to March the Philippines are dominated by the circulation known as the Northeast Monsoon. This is a mass transport of air caused by the increase in size and intensity of the anticyclone overlying Asia. Upon arriving over Luzon the monsoon air has acquired some increased moisture content because of its passage over the warm Kuroshio current. This modification of the polar continental air takes place only in the lower levels - to about 5,000 feet. Above that elevation the air retains its cold, dry and typical continental characteristics. As it moves across Luzon to the west the orographic influence of the Cordillera Central range is felt and most of the moisture content is precipitated so that relatively dry air finally reaches the Lingayen Gulf.

CONCLUSIONS REACHED

In the light of the foregoing considerations it was concluded that the weather to be expected at the time selected for the landings was probably the best which could normally be expected at any time of the year. This was particularly true of beach conditions and soil trafficability. In the words of COMMANDER THIRD

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AMPHIBIOUS FORCE: The decision to make the assault was made by higher echelons, but was heartily seconded by this command in view of the then-existing dry season and the subsequent excellent operating conditions expected to prevail about the target date.

STRATEGIC AND TACTICAL WEATHER CONSIDERATIONS

DURING THE SOFTENING-UP PROCESS

Beginning with the first air strikes on the Manila area of Luzon on 21 and 22 September 1944, the island of Luzon was subjected to an intense pounding by the planes of the various units of Task Force 38. These operations included the bombing and strafing of land targets together with the damaging and sinking of scores of Japanese craft in the harbors and along the sea lanes of the Philippine area.

In the words of COMMANDER SECOND CARRIER TASK FORCE, regarding the Lingayen operation: "The success of the fast carriers in gaining control was contingent on conditions immediately prior to S-day. If the weather between S minus 6 and S-day had been such that the carriers could not have performed their mission, radical changes of plan would have been necessary."

DURING THE APPROACH STAGE

As has been previously stated, plans for approach to the Lingayen area of necessity included consideration of the possible effect of typhoon activity on the transports, landing boats, etc. The presence of quasi-stationary fronts between the point of departure and the landing area was also taken into consideration but as was anticipated, these fronts had no great influence on the operations en route, except for some curtailment of flight operations during the early stages of the advance.

DURING FINAL STAGES

The final stages of the assault, it was realized, would be vitally concerned with swell and surf conditions as well as with the flying conditions then prevailing. A further concern was whether or not wind conditions, as anticipated, would permit the laying of a smoke screen to cover the landing operations.

The significance of the above operational factors is illustrated by the following extracts from action reports:

COMMANDER THIRD AMPHIBIOUS FORCE: "Little or no actual (swell and surf) data on the Gulf was available, but by skillful use of the few known facts these officers constructed ... (a diagram of expected swell and surf in Lingayen Gulf) ... which proved to be quite accurate for the conditions observed and proved very useful to the Force Aerologist in his surf forecasts."

THE COMMANDING OFFICER OF A CVE: "The protection of mountain ranges lessens these winds along the coast, but it should be borne in mind that any operations in the above areas during the winter season will be affected by strong winds, rough seas and heavy swells most of the time."

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THE PRELIMINARY APPROACH

The weather during the approach of the attacking force to Lingayen Gulf was characterized by a series of fronts of a quasi-stationary nature, only two of which seriously affected operations, and that for a period of only two days. This, as explained by COMMANDER THIRD AMPHIBIOUS FORCE, "was not unexpected since the area ...... marked the junction of quasi-stationary fronts from both hemispheres with the Equatorial Front. Reduced visibility, low ceiling, intermittent heavy rain, strong WNW wind and high seas effectively curtailed all air activity, even by land-based aircraft."

Following this short period of unfavorable flying weather, rapid improvement occurred with relatively good flying weather continuing for a few days. During this time overcast conditions prevailed due to intermediate type cloudiness, and occasional areas of very light precipitation were encountered. COMMANDER THIRD AMPHIBIOUS FORCE goes on to say: "The cloud cover was thick enough to keep the ships from heating up during the day while at the same time the actual rainy spells were infrequent enough to afford the troops plenty of opportunity to come on deck for fresh air."

THE FINAL STAGES OF THE APPROACH

The final stages of the approach to Western Luzon began when the convoy came within the range of enemy aircraft, based on Mindanao and the Visayas on 4 January. Perfect cruising weather prevailed on that and the following day, facilitating the fueling of the various ships in the force.

FAVORABLE WEATHER

On 7 January, as will be seen by reference to Plate 1, conditions were ideal, as the high pressure area moving in over the central Philippines resulted in excellent flying conditions, and because of the resulting wind direction caused by the circulation about the "high", carriers had little or no maneuvering to do in order to operate aircraft.

TYPHOON

S minus 1 day began with an increase in wind velocity to about 20 knots from the east as the narrow, low, central neck of Luzon was passed. Reports indicated intense cyclonic activity northwest of Peleliu (Palau group) but it was believed that, in view of the high pressure cell moving off China, any typhoon which might form would be forced to follow a due west course, well south of Lingayen. This assumption proved correct. See Plates 1 to 4 for the development and movement of this typhoon.

By dawn of 9 January the force had completed its approach to the target and was in position to start the assault phase of the operation.

PRELIMINARY AIR SUPPORT OPERATIONS

In the meantime, however, the carrier based aircraft supporting the

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PLATE 1 - 1200 GCT 7 JANUARY 1945.
PLATE 1
1200 GCT 7 JANUARY 1945.

PLATE 2 - 1200 GCT 9 JANUARY 1945.
PLATE 2
1200 GCT 9 JANUARY 1945.

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PLATE 3 - 1200 GCT 11 JANUARY 1945.
PLATE 3
1200 GCT 11 JANUARY 1945.

PLATE 4 - 1200 GCT 13 JANUARY 1945.
PLATE 4
1200 GCT 13 JANUARY 1945.

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operation by diversionary actions were encountering quite different weather in the area between Luzon and Formosa and to the east of Luzon. The following excerpts from an action report illustrate the difficulties with which these forces were faced, due to weather:

BY COMMANDER OF AN AIR SUPPORT TASK UNIT: "Exhaustion of some spares from all ships in the Task Unit, and difficulties experienced in upkeep due to heavy rolling and pitching, reduced aircraft availability.

On Sugar Day it was necessary to jettison 20-500 lb. bombs, 46-100 lb. bombs and 40 rockets from planes which were sent back from the target area without having been assigned a target. At this time 100 lb. bombs were particularly critical, but planes could not be landed aboard loaded due to hazardous landing conditions resulting from heavy seas."

OVER-ALL EFFECT OF WEATHER DURING APPROACH

To sum up briefly the effect of weather on the various forces involved in the operation the following may be pointed out:

1. Flight operations by carriers escorting the convoy were handicapped by weather on only two days during the approach to the target.

2. During the initial stages of the approach to the target cloudy weather and intermittent rain were conducive to the well-being of the troops aboard the transports.

3. Operating conditions were excellent for the convoys and escorting carriers operating on the western side of Luzon protected from the Monsoon by the Cordillera Central mountain range.

4. Extremely adverse flying conditions were encountered by the air support units operating to the east of Luzon and exposed to the full strength of the Northeast Monsoon.

FINAL LANDING OPERATIONS

THE LANDINGS

According to the COMMANDER THIRD AMPHIBIOUS FORCE: "On schedule, at 0930, the first wave of LVT's hit the Lingayen beaches. The expected excellent weather prevailed: skies cloudy with thin broken cirrostratus, scattered alto-cumulus and cumulus; wind force 3 (7 to 10 knots) from the south-southeast and visibility limited to 6 miles by a slight haze aggravated by the dust and smoke kicked up by the pre-H-hour bombing and bombardment.

By mid-morning (of the second day of the assault) the 6 to 8 foot surf at the beaches, resulting from the increased swell, had caused landing operations to come to a halt."

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The cause of the increased swell was the small typhoon which had developed and moved westward from the Peleliu area over the Sulu Sea and thence on to dissipate near the French Indo-China coast. On the third day of the assault the swell diminished and conditions improved rapidly to permit continued landing operations. Plates 1 to 4, prepared from the COMMANDER THIRD AMPHIBIOUS FORCE synoptic maps plainly illustrate the movement and effect of this typhoon. Task Force 38, operating in the South China Sea at this time was to feel the affect of this typhoon upon its air and fueling operations.

SURF OBSERVATIONS

Aerological officers from the THIRD AMPHIBIOUS FORCE and from the SEVENTH AMPHIBIOUS FORCE were airborne in carrier based aircraft over the landing beach to furnish surf observations by radio. The reports were extremely accurate and in the words of the COMMANDER THIRD AMPHIBIOUS FORCE: "these reports were much appreciated by both the Attack Force Commander and by the Commanding General of the XIV CORPS. The latter characterized the reports as clear, concise and very useful, amply justifying the employment of these aerological officers in this type of duty."

CONCLUSION
The vital concern with which weather is viewed in amphibious and air support operations is well stated by the COMMANDER TASK FORCE 38.

"During operations in support of the Luzon invasion, the state of the weather actually placed the accomplishment of effective support by the Task Force in jeopardy, and consequently jeopardized the amphibious operations which were dependent upon the successful operations of the Task Force. The Fleet needs the best aerologist in the Navy, supplied with personnel, equipment and information to enable him to make as accurate forecasts as is humanly possible."

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