Each caisson was placed by the same procedure: After constructing and testing a caisson they pumped out the water so that it floats. Then the caisson was tugged out its construction-dock. The caisson was not immediately put in place but first it was parked several hundred meters away waiting for the right moment. When the water current was low, tugboats pulled the caisson against the flow above the right place on the threshold. During this action the caisson was tugged in an angle of 90 degrees and just before changing of the tide (when the flow was in the opposite direction) the caisson was rotated in the length of the dam. After sinking the caisson on its final position it was filled with sand and embedded in stones. They have calculated that the best moment to start these activities was between April 8 and 25. Other alternatives were March, May and June but In April there was the least chance of stormy weathers and the water flow of the rivers Maas and Waal will be acceptable. May and June were too late because they were not sure if they will have enough time to be finished with this job and the dam was prepared for the storms at the end of that year. Putting the caissons in place was done used as much as possible by daylight. Sinking the caissons should be done when the tide changed from high to low. They had calculated that they needed 20 days. From these 20 days there were 6 days for solving unexpected problems. Placing the caissons started on April 5, after Eastern Sunday. Placing of each caisson must be finished one hour before sunset. It took one day to prepare a caisson for its final journey from the construction-dock to the place in the dam. A day before a caisson was tugged out, they started to pump out the water so that it floats. Generators, floodlights, ropes and other equipment was brought ‘on board’. Even first-aid- and life saving facilities were present. Time and current were the greatest enemies. Everything must be done at the right moment. If something went wrong there was a chance that they must wait till the next day. It took 20 minutes to tug a caisson from the dock to its parking place near the threshold. It took another 20 minutes to pull the caisson above the threshold. For rotating and placing above the final position they had 50 minutes. Finally it took 6 minutes to sink the caisson. During the process they realized that they had miscalculated the exact time for departure. In the Volkerak the high tide started 2 hours later than at sea near the coast. They had misinterpreted the timetables. The result was that the caissons must be tugged out when low tide started. The change that the caisson got stuck on the bottom of the small gully was great. They decided to leave the dock one or two hours sooner. On April 25 at 11:27 hours the last caisson was placed on the threshold, a perfect date, even they had to stop for several day for the strong winds. The positioning of the caissons was done with 7 tug boats with a total of 7.100 hp. The remaining openings between the caissons were filled with sand, stones and gravel. On April 28 at 9:15 hours the 192 slides of 12 special designed sluice-caissons were lowered: the Volkerakdam was closed. Finally the 5.6 million square meters of the dam must be covered with sand. This was done by 3 dredgers: the Queen of Holland, the Concorde and the Versde.