For much of its history military technology has been preoccupied with the mechanics of brute force: explosives, firepower, armour. Its traditional equipment relies heavily on manual operation, usually in extreme environments and is all too often old-fashioned. It has been said that military engineers tend to design for the last war.
There are still, perhaps, fewer electronic systems than might be expected in the general breadth of military hardware. The signs are, however, that times are changing. Recent decades have brought to the armed forces an awareness of the benefits of precise motion control and a newly urgent understanding of the need for modes of efficiency.
The result is that a number of military applications are increasingly making use of motors and drives.Some situations in which electrical devices are used by the military have obvious civilian equivalents. Ventilation units, for example, are a necessary component of field hospitals and other tent-based systems; their variable speed drives work more or less hard to maintain airflow depending on filter pressure, for example, or altitude.
Other motor and drive applications are specifically military in nature. Radar systems, for example, require cooling fans. The radar dishes themselves are positioned by motors that need to accelerate and decelerate rapidly, responding instantly and precisely to control systems. The same is true of the rotational components of gun turrets on top of combat vehicles.
Besides speed and efficiency, military operations occasionally call for low noise levels. It is an essential requirement of anti-submarine vessels, for example, that they restrict, when necessary, underwater-radiated noise to a minimum. Combined diesel-electric and gas propulsion systems enable this. A gas turbine provides the kind of power needed for a ship on the move to achieve top speed; but when it needs to enter stealth mode diesel generators take over. These supply electrical current to the propulsion motors, with variable speed drives modifying the frequency according to the ship’s rate of movement.
The use of VSDs for this purpose is a relatively recent innovation. In older ships variable voltages for the propulsion motors are achieved by using a thyristor converter to rectify the incoming AC. It is incumbent on the designs of both systems to minimise harmonics generated by pulse modulations in order to keep noise signatures as low as possible.
Such hybrid systems bring with them significant energy savings. Naval frigates are now capable of travelling far greater distances between refuellings than ever before. And fuel consumption is a major issue for the armed forces. The United States military is the world’s single largest buyer of oil, getting through hundreds of thousands of barrels a day. Fuel provision strongly influences how much equipment must be taken into a conflict zone and the logistical network that needs establishing once there.
Question marks over the sustainability of this state of affairs have led many to predict a more electrically-powered future for military technology generally and for army vehicles in particular.
Conventional tanks, for example, are sluggish, particularly slow to accelerate, and heavy – liable, as weaponry becomes more powerful, to become yet heavier. Some see these conventional machines as fated by progress to be phased out; and to be replaced by a new generation of smaller, lighter, electrically-propelled vehicles capable of faster acceleration, quieter operation and appreciable fuel savings.
Such vehicles also promise new levels of manoeuvrability. Recent US military-sponsored electric vehicle projects have experimented with situating electric motors entirely within the wheels of combat vehicles, giving them unprecedented torque, traction and speed, as well as the potential for independent movement. And, at the same time, being able to dispense with the mechanical drive shaft on an armoured vehicle’s vulnerable underside eliminates a notorious Achilles’ heel of conventional design.
There is even the possibility that tanks themselves, should their electrical systems become sufficiently developed, might be able to serve as generators of energy out in the field. Traditionally, operating bases are powered by diesel generators which run continuously and can be oversized for the kind of load required by air conditioning and other systems. There has been some effort to remedy this scenario with hybrid generators. As armies’ electrical needs increase and diversify, however, there are those who envisage more radical solutions, such as portable microgrids.
Both the US and UK armed forces are investing significantly in electrification. After all, looking to the future, such investment is a precondition for the adoption of Fourth Industrial Revolution technology. Sensor systems, data processing and elements of automation are all making military work smarter, more efficient and safer. Remote-controlled or fully autonomous robots, to take the most obvious example, have already revolutionised surveillance and maintenance operations.
Progress in this sector is, however, naturally painstaking. Military versions of electronic technology are by design significantly more powerful and more rugged than even their industrial equivalents. The electric drive systems of armoured cars, for example, have about ten times more torque than ordinary consumer models. The US military standard for electronic and electrical parts (MIL-STD-202) dictates that equipment be able to withstand thermal and explosive shocks, attrition by sand and salt, and more.
Nevertheless, as armed forces around the world both progressively reduce their dependence on fossil fuels and bring their range of equipment gradually into the digital age, their use of electric drives and motors is becoming both more varied and more extensive.