Humm...you would they would get in the way; especially given how long they are.

One sees what seem to be hundreds of these things in wartime shots of British cities, the Normandy invasion fleet, etc. Though of some use in deterring low-level strafing runs by fighter aircraft, they would seem to have been less than useful against high-level bombing runs or even a skilled dive-bomber attack (say by Stukas, which the Germans had in plenitude). Still, when one has a near-monopoly on helium, one can afford to indulge in defensive systems of marginal utility, and the morale-boosting effect on the defended population or activity cannot easily be discounted.

Was the U.S. particulary worried about bombers coming from Japan? seems like a long way in 1942, on the prairies in Canada we, like the U.S. worried about incendiary balloons coming over on the newly discovered jetstream, seemed the Japanese had used it as a mode of transporting these devil balloons over to North America.

We lived near Long Beach, California, during WWII and there were many barrage balloons over the oil derricks near Signal Hill. There were cables from the balloons to the ground to deter low flying enemy aircraft which might bomb the oil wells. Sometimes we could see spotlights going back and forth in the sky. It was always an eerie sight, especially at night.