Electrical transformers are the Achilles heel of the U.S. power grid, experts say, because of the threat of physical as well as cyberattacks. The transformers, the largest of which can cost $1 million to $8 million, are key to moving electricity from power-generating plants to consumers across the country, but could be rendered useless by through relatively low-tech attacks, the Wall Street Journal reported Monday. "We've always known that with a couple dollar bullets, you can take out a transformer worth millions of dollars," Steve Newman, vice president of Delta Star Inc. of Lynchburg, Va., told the New York business newspaper. The Journal says it could take the national grid months to recover from a physical attack targeting enough of the nation's 2,000 largest transformers at key points. The newspaper notes an attack by unknown gunmen on a California substation last April damaged 17 large transformers, putting them out of service. With only a few U.S. companies in the business of building transformers, the Journal says it can take weeks or months for replacements to be shipped from overseas. The "greatest vulnerability in the event of a terrorist physical attack on the power system will likely be securing needed replacements of high-voltage transformers," the National Research Council concluded in a 2012 report compiled for the U.S. Homeland Security Department. The resulting blackouts, the report said, "could take weeks, months or even longer" to remedy. The Journal says power companies are trying to prepare for potential widespread problems by pooling spare transformers. It says about 50 utilities have joined a program run by the Edison Electric Institute to share an inventory of backup transformers. But neither the institute nor another industry group, the North American Electric Reliability Corp., will say how many pieces of the critical equipment are on hand or exactly how useful they would be given that transformers are custom-designed for each location. The Journal says the industry is attempting to design a universal transformer to make them interchangeable, but notes that effort is in its early stage.