As work on Nike-X began, high-ranking military and civilian officials began to press for Zeus deployment as an interim system in spite of the known problems.
They argued the system could be upgraded in-place as the new technologies became available.
McNamara was opposed to early deployment, while Congressman Daniel J. Flood would be a prime force for immediate deployment.

McNamara's argument against deployment rested on two primary issues.
One was the apparent ineffectiveness of the system, and especially its benefit-cost ratio compared to other options.
For instance, fallout shelters would save more Americans for far less money, and in an excellent demonstration of his approach to almost any defense issue, he noted:
It is estimated that a shelter system at a cost of $2 billion would save 48.5 million lives.
 The cost per life saved would be about $40.00.
An active ballistic missile defense system would cost about $18 billion and would save an estimated 27.8 million lives.
 The cost per life saved in this case would be about $700. [
He later added that] I personally will never recommend an anti-ICBM program unless a fallout program does accompany it.
I believe that even if we do not have an anti-ICBM program, we nonetheless should proceed with the fallout shelter program.

The second issue, ironically, came about due to concerns about a Soviet ABM system.
The US's existing SM-65 Atlas and SM-68 Titan both used re-entry vehicles with blunt noses that greatly slowed the warheads as they entered the lower atmosphere and made them relatively easy to attack.
The new LGM-30 Minuteman missile used sharp-nosed reentry shapes that traveled at much higher terminal speeds, and included a number of decoy systems that were expected to make interception very difficult for the Soviet ABMs.
This would guarantee the US's deterrent.
If there was a budget choice to be made, McNamara supported Minuteman, although he tried not to say this.

In one particularly telling exchange between McNamara and Flood, McNamara initially refuses to choose one option over the other:
Flood: Which comes first, the chicken or the egg?
Which comes first, Minuteman because he may develop a good Zeus, or our own Zeus?

McNamara: I would say neither comes first.
I would carry on each simultaneously with the maximum rate of activity that each could benefit from.

But later, Flood managed to get a more accurate statement out of him:
Flood: I thought we had broken through this problem in this country, of wanting things to be perfect before we send them to the troops.
I have an enemy who can kill me and I cannot defend myself against him, and I say I should hazard all risks within the rule of reason, to advance this by 2 or 3 years.

McNamara: We are spending hundreds of millions of dollars, not to stop things but to accelerate the development of an anti-ICBM system... I do not believe it would be wise for us to recommend the procurement of a system which might not be an effective anti-ICBM device.
That is exactly the state in which we believe the Zeus rests today.

Flood: ... You may not be aware of it, but you have just about destroyed the Nike-Zeus.
That last paragraph did that.
As work on Nike-X began, high-ranking military and civilian officials began to press for Zeus deployment as an interim system in spite of the known problems. They argued the system could be upgraded in-place as the new technologies became available. McNamara was opposed to early deployment, while Congressman Daniel J. Flood would be a prime force for immediate deployment.
McNamara's argument against deployment rested on two primary issues. One was the apparent ineffectiveness of the system, and especially its benefit-cost ratio compared to other options. For instance, fallout shelters would save more Americans for far less money, and in an excellent demonstration of his approach to almost any defense issue, he noted:
It is estimated that a shelter system at a cost of $2 billion would save 48.5 million lives.  The cost per life saved would be about $40.00. An active ballistic missile defense system would cost about $18 billion and would save an estimated 27.8 million lives.  The cost per life saved in this case would be about $700. [He later added that] I personally will never recommend an anti-ICBM program unless a fallout program does accompany it. I believe that even if we do not have an anti-ICBM program, we nonetheless should proceed with the fallout shelter program.
The second issue, ironically, came about due to concerns about a Soviet ABM system. The US's existing SM-65 Atlas and SM-68 Titan both used re-entry vehicles with blunt noses that greatly slowed the warheads as they entered the lower atmosphere and made them relatively easy to attack. The new LGM-30 Minuteman missile used sharp-nosed reentry shapes that traveled at much higher terminal speeds, and included a number of decoy systems that were expected to make interception very difficult for the Soviet ABMs. This would guarantee the US's deterrent. If there was a budget choice to be made, McNamara supported Minuteman, although he tried not to say this.
In one particularly telling exchange between McNamara and Flood, McNamara initially refuses to choose one option over the other:
Flood: Which comes first, the chicken or the egg? Which comes first, Minuteman because he may develop a good Zeus, or our own Zeus?
McNamara: I would say neither comes first. I would carry on each simultaneously with the maximum rate of activity that each could benefit from.
But later, Flood managed to get a more accurate statement out of him:
Flood: I thought we had broken through this problem in this country, of wanting things to be perfect before we send them to the troops. I have an enemy who can kill me and I cannot defend myself against him, and I say I should hazard all risks within the rule of reason, to advance this by 2 or 3 years.
McNamara: We are spending hundreds of millions of dollars, not to stop things but to accelerate the development of an anti-ICBM system... I do not believe it would be wise for us to recommend the procurement of a system which might not be an effective anti-ICBM device. That is exactly the state in which we believe the Zeus rests today.
Flood: ... You may not be aware of it, but you have just about destroyed the Nike-Zeus. That last paragraph did that.
Nike Zeus