The Philadelphia experiment was fictional, a disinformation scheme to divert humans from exploring the real experiment that occurred. The Philadelphia experiment much in the media is a fraud perpetrated to distract people from pursuing the real Philadelphia experiment, which didn't take place anywhere near Philadelphia. Servicemen were indeed injured, and because the risk of questions existed, the cover story was put up to effectively point any questioners to a dead end. The real experiment with moving between dimensions, which can and does occur naturally on your 3rd Density planet, was done in a warehouse in Kansas - rural, remote, virtually uninhabited because of sparse farm houses and farm hands. The area was inhabited only during planting and harvesting times.
Under intense compression, such as occurs in the center of the Earth, 3rd Density matter emits energy rays which approximate those naturally occurring in 4th Density. These rays escape the core of the Earth in bursts on occasion, thus causing the problems reported in the Bermuda Triangle, for instance, where ships or planes seem to disappear, then reappear. Essentially, the 3rd Density matter is temporarily confused as to its proper rate of vibration, and moves into the 4th Density state. This is akin to what we have done to contactees when they report having moved through walls. However, in the hands of humans, who received information on how to produce this effect from Service-to-Self aliens, this ability proved disastrous. Moving into 4th Density requires more than just bombardment of matter to the point of compression tension. It requires a total shift, and if one expects to return, a total shift back.
The humans conducting this experiment were of such an orientation that they did not care about the servicemen being used, or what might become of them. Rather than hesitate, knowing they did not have all the parameters in place, they proceeded. The servicemen, who were encased in a metal box, were left partially in the 4th Density, along with portions of their container. They were, of course, all dead, but the witnesses of this experiment, and the associates whom the servicemen had just recently been mingling with, were many. The government concocted a repeat experiment, which proceeded part way, enough so that the story as to the results was similar. Additional servicemen were subjected, knowing the probably results, but most of these survived to chat among themselves and their families. All secrets escape, leaks occur, and in this way the investigators would be altogether in the wrong vicinity, and talking to altogether the wrong participants!