In the Russo-Japanese war the machine gun detachments of the Russian cavalry were equipped with _Rexer_ guns which can scarcely be considered machine guns owing to their slow rate of fire and extreme heating of the barrel. Machine guns can be transported upon larger vehicles capable of being unlimbered; they can also be carried on pack horses or other pack animals, and for short distances by men. Although pack animal transportation enables the guns to follow the troops anywhere, the amount of ammunition that can be carried along is limited, and the opening of fire is retarded, since gun and tripod must first be assembled; the opening of fire may even be delayed when a pack animal falls; ammunition cannot be carried on the gun; and the animals get sore backs even if pack saddles are carefully adjusted. 2. THE POWER OF MACHINE GUNS. The machine gun is noted for its adaptability to any terrain, and the constancy of its high rate of fire as compared with that of a body of infantry, which decreases with the range, the diminishing visibility of the target, and prolonged fire. On the other hand, a single jamming can make a machine gun valueless, at least for the time being. For this reason, the Germans employ machine guns only in platoons, as a rule, and the Swiss let both guns of a platoon fire simultaneously only in exceptional cases. Theoretically, the maximum rate of fire of 600 rounds per minute will rarely be attained; and 200-300 rounds per minute will usually suffice against prone targets. In Germany volley and continuous fire are employed; fire by a single piece is used only to ward off patrols when the machine guns do not want to betray their position.[280] [280] The following kinds of fire are used in the countries named below: Austria: Single shots; volleys (20-25 rounds); fire by a single piece. Switzerland: Fire by a single piece; volleys (20-30 rounds); rapid fire (volleys of 100 rounds); and fire at will (both pieces of a platoon simultaneously employing rapid fire). The last-named is only employed in exceptional cases, for example, when the danger is imminent and when favorable opportunities offer. A volley consists of about 25 rounds and is followed by a pause for observing the effect of the fire. It is employed in adjusting the fire upon difficult targets in rolling country. Fire for effect consists, as a general rule, of “continuous fire,” and is interrupted only when the tactical situation requires it. The water in the jacket should be renewed and oiling attended to during the pauses in the fire, whether these grow out of the tactical situation, or are made necessary by technical considerations. The fire is either directed upon a point (concentrated fire), the elevation and direction of the piece being fixed, or it is distributed over the entire target or over a designated part of the same (sweeping, and progressive fire).[281]