10.2.3 The Navy Concept of System
Effectiveness (Ref.
[4])
In the early 1960’s, the Navy developed a system effectiveness
concept which also combines three basic system characteristics: performance,
availability and utilization. It can be expressed as “a measure of the extent
to which a system can be expected to complete its assigned mission within an
established time frame under stated environmental conditions.” It may also be
defined mathematically as “the probability that a system can successfully meet
an operational demand through a given time period when operated under
specified conditions.”
Mathematically it has been formulated as follows:
where:
E_{S} 
= 
index of system effectiveness

P 
= 
index of system performance  a numerical
index expressing system capability, assuming a hypothetical 100%
availability and utilization of performance capability in actual
operation

A 
= 
index of the system availability  a
numerical index of the extent to which the system is ready and capable
of fully performing its assigned mission(s)

U 
= 
index of system utilization  a numerical
index of the extent to which the performance capability of the system
is utilized during the mission 
The components of the Navy model are not as readily computed as
are those of the ARINC and WSEIAC models. The Navy has stated that the terms
PU and A are similar to the WSEIAC terms C and AD (Ref. [5]) and
that PAU can be translated into the analytical terms P_{C} and
P_{T}
where:
P_{C} 

performance capability  a measure of adequacy of design and system
degradation 
P_{T} 

detailed time dependency
 a measure of availability with
a given
utilization 
Thus the Navy model is compatible with the WSEIAC model in the
following way:

f(PAU) = f(P_{C} , P_{T}
) = f(A,D,C) 
(10.12) 
The WSEIAC, Navy and ARINC concepts of system effectiveness are
depicted in Figure 10.21.