The following description of the construction of a submerged bridge is a
condensation of an article originally appearing in the Soviet "Red Star."
It was pointed out in this article that bridges built above the water are
easily observed from the air and on aerial photographs, whereas bridges built
below the surface of the water cannot be detected from altitudes greater
than 900 feet and will not show up on aerial photographs.
Satisfactory conditions for use of submerged bridges are (1) that the
enemy has not previously photographed the area of the crossing, or that the
approaches to the crossing do not reveal the location -- either by the fact that
existing roads are used or new ones constructed along the bank above and below
crossing points; and (2) that there are no sharp changes in water level. It is
sometimes more advisable to construct a submerged bridge within 2 kilometers
of an already existing bridge above water. In such cases the enemy may bomb
the latter, not knowing the submerged bridge is there.
The changes in water level cannot vary more than 10 inches. Any
greater change will either cause the bridge to become impassable or be exposed.
The construction of submerged bridges is somewhat more complicated
than the other types. Working under water increases the time necessary, and
at times divers are needed; this requires special personnel, although
well-trained troops can usually do the job without divers.
The actual construction of this type of bridge does not differ greatly from
that of other bridges except perhaps in that prepared lumber is always necessary.
Care must be taken to have firm approaches; otherwise the disturbance
of the water by crossing vehicles causes the approaches to wash away. This
can be prevented, however, by constructing retaining walls and filling in with
rock or gravel.
It is estimated that a 40-meter (130-foot) bridge with a 60-ton capacity
requires 8 men 24 hours to prepare (but not drive in) the piles. Remarks: Our
Military Attache in Moscow, commenting upon this type of construction, remarks
as follows: "It was noted several days, ago in the Soviet press that such bridges
had been used by the Red Army, and in view of the recent creation of the medal
'Distinguished Pontoneer' it is possible that the use of such bridges has been