Until recently, differences between the two services about the expeditionary role have not been tested, because of:
- The availability of substantial defense resources
- The existence of a conceptual framework (the Cold War) that tended to subordinate the expeditionary function
- The Army focus on heavy land warfare missions in Europe and Korea, and the Marine Corps concentration on the global amphibious mission
- Decentralization in U.S. defense management, wherein the services were not compelled to accommodation themselves to each other
The present threat-poor environment probably is the best opportunity in many years to enrich future strategic planning with a new, rational balance between Army and Marine Corps capabilities, which considers:
- Criteria for planning expeditionary operations in the years ahead
- Force design alternatives
- The relative advantages and disadvantages of Army and Marine Corps forces in a strategic environment where major regional contingencies in a few identifiable regions form the likeliest areas for infrequent ground operations of scope, but where the potential for small-scale incursions probably is worldwide
The Army and Marine Corps have taken different approaches to land warfare, as exemplified in the roles their ground components played in the Gulf War, without clearly foreshadowing how to employ soldiers and Marines more efficiently in austere times. Ideally, what is proper U.S. expeditionary force organization, size, and composition should be debated on strategic merit, as limited by resource constraints. Nevertheless, it is unwise to ignore the effects of service culture and practice and historical precedent. Those traditional factors have been as influential in affecting the composition of expeditionary forces as strategic or budgetary considerations.
The Army and the Marine Corps have evolved in ways reflecting the special military requirements and political and budgetary considerations of earlier periods. Until the turn of the last century, both were specialized services, with little functional overlap beyond convenience-as when Robert E. Lee, then a federal Army officer, used Marines to capture John Brown at Harpers Ferry. In brief, small expeditionary operations designed to end unfriendly local mayhem overseas (e.g., the Tripoli landing in 1803) were Marine Corps operations. Larger expeditionary campaigns more supportive of strategic ends (e.g., the Cuba invasion, Philippine insurrection, and Mexican War) belonged primarily to the Army.
Still, the availability of both kinds of forces almost always produced some Marine involvement in overseas campaigns where the Army was primary. There also was cooperation of sorts in more ambiguous situations, such as the Boxer Rebellion, where both services supplied units, a pattern continued between the two world wars, with both services supplying units to form the U.S. military presence in the China Treaty ports.
U.S. entry on to the global military stage in this century sowed the seeds for a larger, more independent, and more active Marine Corps. In World War I, the 5th and 6th Marine Regiments fought as integral parts of the Army's Second Infantry Division, but Marines considered this experience in cooperation an anomaly. Before, during, and after, Marines were used in expeditionary roles in Cuba, Santo Domingo, Haiti, and Nicaragua.
Using Marines to deal with troubles in the Caribbean between the world wars was easier and more convenient than using soldiers. The Army had been cut back severely in 1919, but the Navy had kept much of the fleet active, with a peacetime complement that included some 25,000 Marines. The Marines with the Navy had the training, bases, transport, and orientation toward small wars. They also had virtually continuous recent experience with them. Some of these, notably the second Nicaragua campaign (1927-33), were more than incursions where a battalion or two restored order and then withdrew. Nicaragua involved 12,000 Marines - almost half the Corps. As they had done in Haiti (1915-33), the Marines ensured the installation of more cooperative local authorities, helped them against armed opposition, and remained in country until local authority could maintain order.
In World War II, the Army and Marine Corps expanded rapidly. The Army had a mission to win a ground war of global scale and to mount a parallel strategic and tactical air effort toward that end. It developed its own sealift and airlift, had its own landing craft, and conducted large and significant amphibious operations-some, such as Normandy and Leyte, much larger than those of the Marine Corps. By the end of the war, Army forces numbered nearly 8.3 million, of which 2.3 million were Army Air personnel. For its part, the Marine Corps grew from 25,000 men organized into light infantry and artillery regiments and air support and observation squadrons into a five-division amphibious force, with each division supported by its parallel aircraft wing. By 1945, it fielded almost 500,000 men. The United States had built itself two armies.
Like most postwar periods, the end of World War II featured drastic reductions in most of the services and most service functions. By the summer of 1948, however, it became clear that the United States would be in a protracted contest with the Soviet Union, a contest for which military forces of all kinds were needed. Unfortunately, the postwar emphasis on strategic nuclear power resulted in a serious shortfall in available expeditionary force components when these first were required in June 1950 for Korea. The Army had barely four divisions immediately available; the Marine Corps less than one. When the Korean War ended in 1953, almost ten U.S. divisions would be on line, of which all but one were Army. Nevertheless, the Marines fought with distinction, under Army command. They also conducted the last amphibious operation of any scope for either service in 1950 at Inchon.
On the other hand, the two Marine divisions in Vietnam were somewhat less under Army control than had been the case in Korea and conducted no significant amphibious operations. Panama was an overwhelmingly Army operation. The Gulf War was more joint; although the Marines were poised to land-and tied down enemy forces with this threat-there were no more amphibious operations.
Smaller expeditionary efforts between World War II and the end of the Vietnam War involved incursions of various sizes, largely for political impact. Between 1945 and 1978, for example, U.S. decision makers turned to the Army least frequently of all the services when wanting to apply a discrete, demonstrative, politically oriented use of force. This is not to gainsay the Army's importance, for the maintenance of a continuous U.S. ground force presence in Europe and Korea may have been the most important way in which U.S. armed forces have served political objectives-by conditioning the expectations of foreign leaders to such an extent that discrete employment of force has been needed less often.
All told, during that period Army ground combat forces took part in 39 incidents. When it did become involved, the Army typically did so in force. More than one full division was used in more than one-fourth of the incidents in which ground combat forces were employed. Four of these major incidents occurred between 1968 and 1973; four others between 1958 and 1962. Six of these multiple division involvements took place in Europe, generally stemming from controversies over Berlin.
There were nine instances of Army ground force operations involving multiple battalion through full brigade size units, but the last of these occurred in 1964. This probably reflects constraints on Army resources as a result of the deployment of considerable forces to Vietnam while maintaining large forward deployments in Europe and Korea. Indeed, manpower was so tight that troop levels in Europe had to be drawn down during the Vietnam buildup. Given these strains on manpower, Army ground combat forces seem to have been used elsewhere during the Vietnam War only for the most serious contingencies-those in which larger than brigade-size forces were required.
Marine Corps ground combat forces got turned to more often for small-scale operations abroad, taking part in 77 incidents between World War II and the end of the Vietnam War. In all but six of these, they were moved to the region of crisis or already had been deployed in that region on amphibious ships. The use of Marines in limited, politically oriented operations is consistent with the Corps' central self-perception. In addition, Marines are equipped, trained, and organized for quick reaction, limited operations, and flexible response. Most important, Marine Corps units have been maintained afloat in the Mediterranean, Western Pacific, and often in the Caribbean throughout the post-World War II period. For these reasons, the Marine ground units used in these incidents most frequently were multi-company or battalion sized-the kinds of units maintained afloat.
As the new century appears on the horizon, resource austerity and a growing emphasis on expeditionary missions suggest a sharpened debate about Army-Marine Corps cooperation, complementarity, or competition. Issues will include:
- Divisions of labor (by geography, by mission, and by capability)
- Suitability and adequacy of service doctrine, organization, and logistics and lift for particular tasks
- Relevance of service warfighting concepts for the 21st century strategic environment
- Relative costs of alternative force postures
- Comparative staying power and flexibility
- Availability and efficiency of air support, air defense, and other combat support
- Adaptability of different service units to existing and possible command-and-control arrangements, including questions of subordination
- Comparative requirements of each service for heavy versus light, ready versus reserve, and other force alternatives in the expeditionary mission
Some of the boundaries of these arguments already are clear. The Marine Corps no longer is a small service in comparison to the Army-today's Corps is about two-fifths the size of the Army. In addition, the past 50 years suggest strongly that no likely contingency will require more than nine U.S. divisions, of which no more than two will be Marines. Those factors suggest a ground force planning ratio for a bounding case-the largest expeditionary efforts.
For all cases, including smaller ones, experience since the beginning of this century suggests several other conclusions about the use of soldiers and Marines in expeditionary operations:
- The most conveniently available appropriate force tends to be the one that gets used.
- Ascribed specialization usually is less important than readiness and availability.
- Most expeditionary operations are small scale and tend to be Marine Corps operations, especially in areas where Marines already were nearby.
- Operations that seem likely to become large scale tend to be Army led.
- Neither service wants to be left out entirely.
The expeditionary mission can be split - by size, distance to the target, and anticipated logistics factors. Indeed, more than in the past, it may have to be shared, and to the extent possible, sharing should be planned in advance. There will not be enough people or lift otherwise. Thus, for the Corps and for the Army, planning how to share is worth more effort that planning how to compete.