The purpose of any river crossing is to project combat power across a water obstacle to accomplish a mission. A river crossing is a unique operation. It requires specific procedures for success because the water obstacle prevents normal ground maneuver. It also requires detailed planning and control measures and different technical support than other tactical operations require. The nature and size of the obstacle, the enemy situation, and available crossing assets limit the tactical commander's options.
The challenge is to minimize the river's impact on the commander's ability to maneuver. The force is vulnerable while crossing, as it must break its movement formations, concentrate at crossing points, and reform on the far shore before continuing to maneuver. The tactical commander cannot effectively fight his force while it is split by a river. He must reduce this vulnerability by decreasing his force's exposure time. The best method is to cross rivers in stride as a continuation of the tactical operation, whether in the offense or retrograde. Only as a last resort should the force pause to build up combat power or crossing means before crossing.
Throughout history, armies crossed rivers to engage or flee from enemy forces. The ancient Persian Army built bridges during their invasion of Greece in the fifth century BC. Herodotus drew many parallels between Xerxes and Darius, notably their building of bridges across the Bosporus.
In 513 BC Darius the Great embarked on the Scythian expedition, the first historic attack of Asia on Europe. According to Herodotus, in Darius assembled 700,000 men and 600 ships to the Bosporus, where a bridge of boats had been constructed. To cross the Danube delta into Thrace (in modern Romania), in 513 BC Darius built a massive bridge of boats. Miltiades, the Athenian despot, advised the leaders who were left at the Danube bridge to destroy it and leave Darius to his fate. This story is improbable, as Darius left Miltiades in possession of the Chersonese for some twenty years longer, though Persian forces were frequently in the neighbourhood. Darius was planning a second invasion of Greece when he died, leaving the throne to his son Xerxes, under whom the war with Greece was carried to a disastrous climax.
The army of Xerxes was certainly the greatest that had hitherto been assembled in the world. In 480 BC the army of Xerxes prepared to cross the Hellespont, the narrow strait in Turkey which separated Asia from Europe. This was an enormous undertaking, for the bridge had to be over a mile long. Xerxes had a boat bridge built, with each boat attached to the next with planks. According to Herodotus, " ... fifty-oared ships and triremes were set side by side, about three hundred and sixty to form the Euxinian bridge, and about three hundred and fourteen to form the other bridge, all of them at right angles to the Pontus and parallel to the Hellespont..." The boat bridge was nearly complete when winds and rough seas broke it apart, but the second attempt to build a bridge was successful. Embankments of timber, stone and packed earth were laid across the ships' decks to form roadways. Eventually the entire Persian army - said to number a million men but probably only a tenth that number -crossed it.
In the fourth century BC ancient Macedonia first used professional engineers to facilitate movement across rivers.
Various ancient Roman armies frequently conducted river crossings to engage other armies. As any Latin student who has read The Battle for Gaul will recall, in 55 B.C. Julius Caesar constructed a bridge across the upper Rhine in 10 days. He built the bridge not to conquer but to intimidate. As the restless German tribes on the far bank watched the soldiers complete an engineering feat far beyond their comprehension, they realized the futility of resisting the power of Rome. After 18 days of marching about on the opposite shore, Caesar, having never fought a battle, recrossed the Rhine and dismantled the bridge behind him. He had made his point.
Dying out after the fall of Rome and Constantinople, river crossings again became common events when armies became mobile during the eighteenth century. Armies frequently performed river crossings during the Napoleonic Wars and the two World Wars. More recently, the Israeli Army crossed the Suez Canal to encircle the Egyptians after the Egyptians first crossed the canal during the 1973 Yom Kippur War.
During the Civil War, Army engineers built pontoon and railroad bridges. In December 1862 Union Army enginneers laid six pontoon bridges across the Rappahannock River, under devastating fire from Confederate sharpshooters, in support of the Union attack on Fredericksburg, Virginia.
The 2,170-foot pontoon bridge, which Union engineer troops laid across the James River in June 1864 as the Army of the Potomac approached Petersburg, Virginia, was the longest floating bridge erected before World War II. The banks of the James River became the focus of Grant's strategy to attack Petersburg and cut off the Confederate army's supply line. Federal engineers of the Pontoon Corps began building the massive pontoon bridge across the James below Wilcox's landing the morning of 14 June, and the bridge was completed about midnight of the 14th. The remarkably stable and steady pontoon bridge was constructed of 68 boats with wooden bridge planks tied to them, spanning over 13 fathoms of water. Grant's Army of the Potomac moved some 45,000 men and 30,000 horses and cattle across the river, successfully deceiving Lee and the Army of Northern Virginia. Thousands of soldiers crossed the James River via the bridge as Grant sought to shift his army quickly south of the river to threaten the rail supply running through Petersburg. Refered to as "Grant's Crossing," the temporary bridge was a glorious feat of engineering. Confederate General E. Porter Alexander called it "The greatest [bridge] . . . the world has seen since the days of Xerxes."
During late March of 1945, the US Third Army under Gen. Patton, began its famous bridging and crossing operations of the Rhine. After the completion of the Battle in The Ardennes, Patton and his Army turned to the south and east attacking toward the Rhine. Without the luck of the 9th Armored Division, further to the north, who were able to capture the only intact bridge across the Rhine at Remagen, Patton's Third Army faced the necessity of bridging the wide river with their own resources. There had been a total of 22 road and 25 railroad bridges spanning the Rhine into Germany, but with the exception of the Remagen Bridge, they had all been destroyed.
The first unit to cross was the 5th Infantry Division that used assault rafts to cross the raging Rhine at Oppenheim (west of Darmstadt and south of Mainz) in the early morning hours of March 23. The 150th Engineer Combat Battalion (ECB) inflated the floats for the bridge in the rear area, moved them to the river in trucks, and by daybreak had assembled them into rafts. By 1880 that evening, a class 40 M-2 treadway bridge was taking traffic. The following day, a second 1,280 foot class 24 bridge was completed in the same area. It was later upgraded to a class M-40 bridge. Without the benefit of aerial bombardment or artillery preparation, units landed quickly and established a beachhead that was seven miles wide and six miles deep in less than 24 hours. Several amphibious tanks of the 748th Tank Battalion crossed with the men of the 5th ID. When daylight came, the Luftwaffe attacked the enclave with 154 aircraft in an attempt to dislodge the foothold on the east bank. Effective anti-aircraft fires brought down 18 of the attacking planes and destroyed 15 more.
By March 27, five divisions with supporting troops and supplies had crossed the three bridges constructed at Oppenheim. The entire 6th Armored Division crossed in lass than 17 hours. During the period of March 24-31, a total of 60,000 vehicles passed over these bridges. After consolidating on the east bank, the Third Army continued its drive to the east, capturing Darmstadt on March 25, and arriving in Frankfurt the following day. Working as a well-coordinated unit, the Third Army relied upon trained veteran soldiers, dedicated leadership, an excellent working relationship with the XIX Tactical Air Command, a logistical train that moved all classes of supplies and personnel replacements quickly to the front.
Operation JOINT ENDEAVOR began in the fall of 1995 under the worst Balkan winter and flooding of the Sava River in 70 years. The Sava River crossing was an engineering feat that will go unmatched for some time. A ribbon float bridge was deployed by the Army's 1st Armored Division to cross the Sava River between Croatia and Bosnia and Herzegovina. The pontoon bridge crossing the Sava river between Croatia and Bosnia was 620 meters long and consisted of 63 individual pieces. This was the longest assault float bridge in military history -- and under the worst conditions. The river crossing was exacerbated by severe flooding and an international pressure to cross the river to meet time constraints of the Dayton Peace Accord. The Sava river begins in Croatia and continues into Serbia. The river forms a good part of the Northern Bosnia-Herzegovina border with Croatia. The 130th Engineer Brigade controlled bridging operations over the Sava River from January to May 1996. This included the two floating bridges upstream from Brcko at Zupanja. After building the bridge in December, the 130th Engineer Brigade's 502nd Engineer Company maintained the bridge and received traffic -- a total of 20,000 vehicles. They disassembled the bridge in April 1996.
Although technology has improved crossing means, the basic fundamentals of attacking an enemy across a river have not changed since ancient times. A commander who violates these fundamentals becomes frustrated and fails to cross his force.
Such was the case of the United States (US) 36th Infantry Division at the Rapido River in Italy during World War II. The Germans defeated the 36th Division. The division lost 1,681 soldiers in the two regiments that tried to cross the Rapido River. Attached units suffered several hundred additional losses. The Germans took 500 American prisoners during the two-day battle. The Germans suffered few losses and held their positions along the river.
Effective C2 is essential for a successful river-crossing operation. Normally, during a river-crossing operation, both a division and a brigade are task-organized with unfamiliar assets (such as bridge companies). This, besides the requirement to pass a large volume of traffic across a water obstacle quickly, makes effective C2 very difficult.
The planning and execution of deliberate river-crossing operations has become a lost art. Few units have the opportunity to conduct a deliberate river-crossing operation as part of their home-station training. This is, in part, due to the loss of the divisional Assault Float Bridge companies. The engineer community must also impress upon maneuver commanders that a deliberate river crossing is a complex combined arms operation, and it takes the entire combined arms team to plan and execute a successful river-crossing operation.
Corps and divisions typically task subordinate units to conduct river-crossing operations without giving them sufficient resources and support. Corps must allocate sufficient resources to crossing divisions; not every division needs to conduct an opposed river crossing; therefore, not every division needs river-rossing assets. Likewise, divisions must allocate sufficient resources and support to crossing brigades. Typically, divisions will allocate assets down to the crossing brigades, and what is supposed to be a division deliberate crossing turns into separate brigade crossings that are not synchronized with the division's plan. Corps and divisions have a planning and resourcing responsibility for river-crossing operations. For instance, corps will develop the deception plan and resource this plan for a division deliberate river crossing. Corps and divisions must also assist in setting the conditions for subordinate unit river-crossing operations. An example of this would be the corps providing additional artillery and aviation assets to conduct deep attacks against enemy artillery which could influence the crossing sites.
River crossings are a division responsibility. Normally, they are planned in detail at division level. The corps has specific fundamental planning and resource responsibilities for river-crossing operations, especially for deliberate crossings of large water obstacles.
The corps develops the river-crossing plan concurrently with the scheme of maneuver for the entire operation. The goal of river crossing, whether an offensive or retrograde crossing, is movement of corps units across a water obstacle with minimum impact on the corps' fighting ability.
The corps selects the bridgehead location for an offensive river crossing. The bridgehead is the area on the far bank the corps must secure to press the fight. It must provide space for combat, CS, and critical CSS elements necessary for the attack. The location must have the following properties:
- Large enough to maneuver and deploy the force required for mission continuance.
- Facilitate continuation of the operation.
Securing the bridgehead requires control of an area on the exit bank large enough to accommodate the assault and essential support elements of the crossing force. In addition to accommodating the crossing force and facilitating future operations, the size of the bridgehead may be determined by defensive characteristics of the terrain. Not only must the enemy be defeated at the bridgehead, but it must also be prevented from effectively counterattacking the crossing force and/or destroying crossing sites once the bridgehead is secured. Thus, defensible terrain and space within the bridgehead are required in a defense against an enemy counterattacking to regain control of the river bank.
The bridgehead's depth depends on terrain considerations and the corps' scheme of maneuver. If the division(s) conducting the crossing continues the attack beyond the bridgehead, they use a shallow bridgehead (about 30 kilometers).
If the corps intends to pass a follow-on division through the bridgehead, it will need more depth (40 to 50 kilometers). The river-crossing operation is complete once the bridgehead is secure, the necessary elements have moved to the far shore, and the river obstacle no longer limits the continuation of the attack.
In some cases, the division conducting the assault crossing of the river will not have the combat power, or is not organized for combat. The corps must designate a division intermediate objective or phase line where the lead division can reorganize, build up combat power, or commit trailing forces.
The corps determines if its divisions cross the river on a wide front, involving two or more divisions, or on a narrow front, involving one division. Usually, a crossing on a wide front is preferred. It projects combat power more rapidly and keeps the corps dispersed. A corps may cross on a narrow front if the scheme of maneuver requires it, the terrain dictates, or the corps does not have the equipment necessary for a wide-front crossing.
The corps controls much of the special equipment and support units that maneuver units require for river crossings. A one-division crossing of a large river usually requires the following corps units:
- Two or more corps combat engineer battalions (one battalion per brigade crossing area).
- One or more engineer assault bridge companies (depending on the river's width and the crossing frontages).
- One or more smoke generator and NBC reconnaissance companies (depending on the crossing frontages).
- One MP company with augmentation from a corps MP company to support the traffic control plan (at least one platoon per brigade crossing area).
- One or more ADA battalions (depending on the crossing frontages and the number of bridge and raft sites) and possibly defensive counter air support.
Combat service support for divisions conducting river crossings is similar to sustainment operations during offense or defense. Make transportation support for engineer units and bridging material a top priority. Maintenance of bridging equipment and fuel requirements are secondary considerations.
Other corps support to maneuver units could include specific intelligence-collection concerning river conditions or helicopter support to a division or brigade conducting air assaults on the far shore.
Assault forces close on the water obstacle and cross rapidly by any means available. Infantry elements establish local security on the exit bank to permit development of the crossing sites. Initial crossings may be limited to pneumatic assault boats and amphibious vehicles while tanks provide support from overwatching positions. Army aviation assets may lift the assault force over the obstacle with the assault across the water.
The major concerns of the crossing and assault force commanders during any attack that includes a water obstacle are vulnerabilities of forces on the exit bank and a rapid advance to secure objectives. The latter is the overriding consideration; hence planning commences at the objectives and projects back toward the river. An accurate assessment of the enemy's expected counterattacks and indirect fire barrages is integrated into planning. This is particularly significant during early stages of the advance because the assault force is temporarily divided by the river, thus diminishing its combat power potential. To counter probable enemy reaction, counterfires and aerial attacks augment other planned fires to ensure the necessary rapid advance to overwhelm the enemy.
One corps ribbon bridge company is capable of supporting a brigade task force crossing. It also can support a brigade unopposed crossing, if it has sufficient bridging to bridge the river. A brigade or divisional crossing requires additional corps bridge companies. Normally, each task force requires about one bridge company's assets to support crossing sites. A crossing brigade requires a minimum of two companies. This depends on river width and the number of crossing sites required to support the scheme of maneuver. If the brigade is conducting an opposed river crossing, the corps combat engineer battalion commander becomes the crossing area engineer. The engineers supporting the assault force are separate and distinct from the engineers conducting the crossing. They are task organized with the bridgehead and breakout forces oriented on the far shore combat missions, not the tasks associated with the river crossing.
The hasty river crossing is one of the most complicated and dangerous operations to execute. It is dangerous because it is easy for either the attacker or defender to locate the positions of the enemy. Similarly, air assets are able to identify the target area easily as they navigate along the river line. Therefore, the commander must be prepared to execute this operation under fire. His leadership is crucial in moving the forces across the river and assaulting the bridgehead objectives. Assault forces advance quickly, without extensive reorganization, from crossing areas to objectives within the bridgehead. The enemy, given time, attempts to halt the advance with strongpoint defenses, heavy artillery fires, and counterattacks.
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