In the late 1940s, the Board of Governors wanted to improve and modernize Baltusrol's golf courses in order to attract another U.S. Open Championship. In 1948, the Board retained Robert Trent Jones to oversee the work. Francis Ouimet, who as a 19-year-old golfer in 1913, shocked the golf world by winning the U.S. Open at The Country Club in Brookline, acted in an advisory capacity on the project.

The Lower Course was lengthened and modernized by Jones without detriment to the original Tillinghast design. Some 400 yards were added to the length of the course, making it more commensurate with the power game that was evolving since Baltusrol last had hosted the Open in 1936. In stretching the course to 7,000 yards, Jones added a number of fairway bunkers to emphasize the need for tee-shot accuracy. He also consolidated or enlarged bunker complexes around greens, and eliminated bunkers that were no longer relevant. As had been predicted by Tillinghast 30 years earlier, the Lower would lose its teeth eventually as course conditions improved and the golf ball along with precision balanced, steel-shafted clubs brought more power to the game. Indeed, Tillinghast was quite prescient!

Jones's most significant change was to the fourth hole. It was lengthened by nearly 70 yards with two new tees of 165 yards and 186 yards. In designing the fourth, Tillinghast had installed a pond which required a full carry to reach the green. Jones strengthened the hole with a longer carry, a terraced green, and a re-shaping of the bunkers behind the green. It was Jones who added the distinctive rock wall guarding the green, as the predecessor facade was made of logs and compacted earth.

The result is a stunning par-3 that stands out as Baltusrol's signature hole and one of the top ranked holes in the world of golf.

But the story of the "Famous Fourth" is not complete without recounting what happened when the hole was opened for play in 1952. Jones was criticized by members for making their fourth hole too difficult. "Let's go play the hole and see if there is anything that needs to be done," Jones suggested as he led the principal critic along with head professional Johnny Farrell and C.P. Burgess, Chairman of the 1954 Open Championship, to the fourth tee. They all struck shots. After Farrell and the two members hit the green, Jones struck his 4-iron and sank it for a hole-in-one! "Gentlemen, I think the hole is eminently fair," the architect said.