Found in a FURUNO-made GMDSS-Guide from 1996 (H. Busch)

Comparison of old distress system and GMDSS
Reliance on ship in vicinity
Wordwide coverage
Because of the inherently limited range of
transmissions on the previous commonly
used distress and calling frequ. of 500
and 2182 kHz, there was no guarantee
that a call for assistance would be
received if the vessel was more than a
few hundred miles from a coast station.
Assistance would only be available if
another vessel was within range.
The GMDSS vessel carry the communi-
cations equipment appropriate to the
Sea Area in which they are operating. 
Having the capability to choose a long
range method when necessary, a call
for assistance can reach a coast station
and will have a greater chance of being
heard by other ships.
Special skill to operate
Simple & automatic operation
Radio Officers send a distress call in
Morse Code on 500 kHz through compli-
cated operations, such as the switching
and adjustment of transmitters.
successful distress attempt relies heavily
on his skill.
On the contrary, the GMDSS equipment
provides easy operation in an emergency
situation just by pressing the distress
buttonin Inmarsat Maritime MES or DSC.
In addition, a float-free EPIRB automa-
tically transmits a distress alert and
Eqipment compatibility
Equipment compatibility
With the previous system, it was only
possible for the vessel in distress to ask
for assistance of other vessels in the vici-
nity as the communication equipment
has limited ranges. Another problem was
incompatibility of communication between
a telephony vessel and a telegraphy vessel.
All GMDSS vessels carry standard equipment
for the Sea Area they are in, operating on
the same frequencies and modes; thus, the
compatibility between them is completely
No doubt, GMDSS has the capability of being a good and easy to handle alerting system in distress cases. But there should be much more skill! Only somebody who calls "switching and adjustment of transmitters" a "complicated operation" can produce that much false alarms  - just by an "easy operation as pressing the distress button." Within one year more false alarms are transmitted, than the old distress system generated all together in it's nearly 10 decades.
Communication between "telephony-" and "telegraphy vessels" was not incompatible. All "telegraphy vessels" carried the "2182-watch-receiver" on the bridge, they were able to switch 2182 kHz on their main-transmitter and receiver and thus were also able to transmit/receive the 2-tone-alarm for 2182 kHz and answer distress-calls = 
H. Busch +
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Version: 19-Jul-01 / HBu