"Early Bird", a short story by Theodore R. Cogswell and Theodore L. Thomas, was first published in 1973, not the '50s, but it fits your plot description very well. There is a Wikipedia page for this story.
Here is an excerpt:
The spermatazoa reached an altitude of half a kilometer before achieving homing ability. They circled, losing altitude until their newly activated homing mechanisms picked up the high-frequency emissions of the distant egg. Then tiny jets began pouring carbon dioxide, and flattened leading edges bit into the atmosphere as they arced toward their objective.
Each was a flattened cylinder, twenty meters long, with a scythe-shaped sensing element protruding from a flattened head, each with a pair of long tails connected at the trailing edge by a broad ribbon. It was an awesome, armada, plowing through the turbulent atmosphere, homing on the distant signal.
As the leaders of the sperm swarm appeared over the horizon, Gog's sensors locked in. The selection time was near. Energy banks cut in and fuel converters began to seethe, preparing for the demands of the activated weapons system. At twenty kilometers, a long-range beam locked in on the leading spermatazoon. It lacked evasive ability and a single frontal shot fused it. Its remnants spiraled to the surface, a mass of carbonized debris interspersed with droplets of glowing metal.
The shock of its destruction spread through the armada and stimulated wild, evasive gyrations on the part of the rest. But Gog's calculators predicted the course of one after another, and flickering bolts of energy burned them out of the sky. None was proving itself fit to survive. Then, suddenly, there was a moment of confusion in her intricate neural network. An intruder was approaching from the wrong direction. All her reserve projectors swiveled and spat a concentrated cone of lethal force at the rogue gamete that was screaming down through the atmosphere. Before the beam could take effect, a milky nimbus surrounded the approaching stranger and it continued on course unharmed. She shifted frequencies. The new bolt was as ineffective as the last. A ripple of excited anticipation rippled through her great bulk. This was the one she'd been waiting for!