diff --git a/icu4c/source/data/makedata.mak b/icu4c/source/data/makedata.mak
index 2391e29bdc5..7189ba984aa 100644
--- a/icu4c/source/data/makedata.mak
+++ b/icu4c/source/data/makedata.mak
@@ -229,7 +229,7 @@ ALL : GODATA "$(DLL_OUTPUT)\$(U_ICUDATA_NAME).dll" "$(TESTDATAOUT)\testdata.dat"
 #
 # testdata - nmake will invoke pkgdata, which will create testdata.dat 
 #
-"$(TESTDATAOUT)\testdata.dat": $(ICUDT)ucadata.dat $(TRANSLIT_FILES) $(RB_FILES)  {"$(ICUTOOLS)\genrb\$(CFG)"}genrb.exe
+"$(TESTDATAOUT)\testdata.dat": $(ICUDT)ucadata.icu $(TRANSLIT_FILES) $(RB_FILES)  {"$(ICUTOOLS)\genrb\$(CFG)"}genrb.exe
 	@cd "$(TESTDATA)"
 	@echo building testdata...
 	nmake /nologo /f "$(TESTDATA)\testdata.mk" TESTDATA=. ICUTOOLS="$(ICUTOOLS)" PKGOPT="$(PKGOPT)" CFG=$(CFG) TESTDATAOUT="$(TESTDATAOUT)" ICUDATA="$(ICUDATA)" TESTDATABLD="$(TESTDATABLD)"
@@ -244,17 +244,17 @@ BRK_FILES = "$(ICUBLD)\$(ICUDT)sent.brk" "$(ICUBLD)\$(ICUDT)char.brk" "$(ICUBLD)
 #  move the .dll and .lib files to their final destination afterwards.
 #  The $(U_ICUDATA_NAME).lib and $(U_ICUDATA_NAME).exp should already be in the right place due to stubdata.
 #
-"$(DLL_OUTPUT)\$(U_ICUDATA_NAME).dll" : "$(ICUTOOLS)\pkgdata\$(CFG)\pkgdata.exe" $(CNV_FILES) $(BRK_FILES) "$(ICUBLD)\$(ICUDT)uprops.dat" "$(ICUBLD)\$(ICUDT)unames.dat" "$(ICUBLD)\$(ICUDT)unorm.dat" "$(ICUBLD)\$(ICUDT)cnvalias.icu" "$(ICUBLD)\$(ICUDT)tz.dat" "$(ICUBLD)\$(ICUDT)ucadata.dat" "$(ICUBLD)\$(ICUDT)invuca.dat" $(ALL_RES) "$(ICUBLD)\$(ICUDT)icudata.res" "$(ICUP)\source\stubdata\stubdatabuilt.txt"
+"$(DLL_OUTPUT)\$(U_ICUDATA_NAME).dll" : "$(ICUTOOLS)\pkgdata\$(CFG)\pkgdata.exe" $(CNV_FILES) $(BRK_FILES) "$(ICUBLD)\$(ICUDT)uprops.icu" "$(ICUBLD)\$(ICUDT)unames.icu" "$(ICUBLD)\$(ICUDT)unorm.icu" "$(ICUBLD)\$(ICUDT)cnvalias.icu" "$(ICUBLD)\$(ICUDT)tz.icu" "$(ICUBLD)\$(ICUDT)ucadata.icu" "$(ICUBLD)\$(ICUDT)invuca.icu" $(ALL_RES) "$(ICUBLD)\$(ICUDT)icudata.res" "$(ICUP)\source\stubdata\stubdatabuilt.txt"
 	@echo Building icu data
 	@cd "$(ICUBLD)"
  	@"$(ICUTOOLS)\pkgdata\$(CFG)\pkgdata" -e $(U_ICUDATA_NAME) -v -m dll -c -p $(ICUPKG) -O "$(PKGOPT)" -d "$(ICUBLD)" -s . <<pkgdatain.txt
-$(ICUDT)uprops.dat
-$(ICUDT)unames.dat
-$(ICUDT)unorm.dat
+$(ICUDT)uprops.icu
+$(ICUDT)unames.icu
+$(ICUDT)unorm.icu
 $(ICUDT)cnvalias.icu
-$(ICUDT)tz.dat
-$(ICUDT)ucadata.dat
-$(ICUDT)invuca.dat
+$(ICUDT)tz.icu
+$(ICUDT)ucadata.icu
+$(ICUDT)invuca.icu
 $(CNV_FILES:.cnv =.cnv
 )
 $(ALL_RES:.res =.res
@@ -275,25 +275,25 @@ $(BRK_FILES:.brk" =.brk"
 #      TODO:  set up an inference rule, so these don't need to be written out one by one...
 #
 
-"$(ICUBLD)\$(ICUDT)char.brk" : "$(ICUBRK)\char.txt" "$(ICUBLD)\$(ICUDT)uprops.dat"
+"$(ICUBLD)\$(ICUDT)char.brk" : "$(ICUBRK)\char.txt" "$(ICUBLD)\$(ICUDT)uprops.icu"
 	genbrk -r "$(ICUBRK)\char.txt" -o "$(ICUBLD)\$(ICUDT)char.brk"
 
-"$(ICUBLD)\$(ICUDT)word.brk" : "$(ICUBRK)\word.txt" "$(ICUBLD)\$(ICUDT)uprops.dat"
+"$(ICUBLD)\$(ICUDT)word.brk" : "$(ICUBRK)\word.txt" "$(ICUBLD)\$(ICUDT)uprops.icu"
 	genbrk -r "$(ICUBRK)\word.txt" -o "$(ICUBLD)\$(ICUDT)word.brk"
 
-"$(ICUBLD)\$(ICUDT)line.brk" : "$(ICUBRK)\line.txt" "$(ICUBLD)\$(ICUDT)uprops.dat"
+"$(ICUBLD)\$(ICUDT)line.brk" : "$(ICUBRK)\line.txt" "$(ICUBLD)\$(ICUDT)uprops.icu"
 	genbrk -r "$(ICUBRK)\line.txt" -o "$(ICUBLD)\$(ICUDT)line.brk"
 
-"$(ICUBLD)\$(ICUDT)sent.brk" : "$(ICUBRK)\sent.txt" "$(ICUBLD)\$(ICUDT)uprops.dat"
+"$(ICUBLD)\$(ICUDT)sent.brk" : "$(ICUBRK)\sent.txt" "$(ICUBLD)\$(ICUDT)uprops.icu"
 	genbrk -r "$(ICUBRK)\sent.txt" -o "$(ICUBLD)\$(ICUDT)sent.brk"
 
-"$(ICUBLD)\$(ICUDT)title.brk" : "$(ICUBRK)\title.txt" "$(ICUBLD)\$(ICUDT)uprops.dat"
+"$(ICUBLD)\$(ICUDT)title.brk" : "$(ICUBRK)\title.txt" "$(ICUBLD)\$(ICUDT)uprops.icu"
 	genbrk -r "$(ICUBRK)\title.txt" -o "$(ICUBLD)\$(ICUDT)title.brk"
 
-"$(ICUBLD)\$(ICUDT)word_th.brk" : "$(ICUBRK)\word_th.txt" "$(ICUBLD)\$(ICUDT)uprops.dat"
+"$(ICUBLD)\$(ICUDT)word_th.brk" : "$(ICUBRK)\word_th.txt" "$(ICUBLD)\$(ICUDT)uprops.icu"
 	genbrk -r "$(ICUBRK)\word_th.txt" -o "$(ICUBLD)\$(ICUDT)word_th.brk"
 
-"$(ICUBLD)\$(ICUDT)line_th.brk" : "$(ICUBRK)\line_th.txt" "$(ICUBLD)\$(ICUDT)uprops.dat"
+"$(ICUBLD)\$(ICUDT)line_th.brk" : "$(ICUBRK)\line_th.txt" "$(ICUBLD)\$(ICUDT)uprops.icu"
 	genbrk -r "$(ICUBRK)\line_th.txt" -o "$(ICUBLD)\$(ICUDT)line_th.brk"
 
 
@@ -314,6 +314,7 @@ CLEAN : GODATA
 	-@erase "*.dat"
 	-@erase "*.exp"
 	-@erase "*.obj"
+	-@erase "*.icu"
 	-@erase "*.lib"
 	-@erase "*.mak"
 	-@erase "*.res"
@@ -359,20 +360,20 @@ res_index {
 	@echo Creating data DLL version information from $**
 	@rc.exe /i "..\..\..\..\include" /r /fo $@ $**
 
-# Targets for unames.dat
-"$(ICUBLD)\$(ICUDT)unames.dat": "$(ICUUNIDATA)\*.txt" "$(ICUTOOLS)\gennames\$(CFG)\gennames.exe"
+# Targets for unames.icu
+"$(ICUBLD)\$(ICUDT)unames.icu": "$(ICUUNIDATA)\*.txt" "$(ICUTOOLS)\gennames\$(CFG)\gennames.exe"
 	@echo Creating data file for Unicode Names
 	@set ICU_DATA=$(ICUBLD)
 	@"$(ICUTOOLS)\gennames\$(CFG)\gennames" -1 -u $(UNICODE_VERSION) "$(ICUUNIDATA)\UnicodeData.txt"
 
-# Targets for uprops.dat
-"$(ICUBLD)\$(ICUDT)uprops.dat": "$(ICUUNIDATA)\*.txt" "$(ICUTOOLS)\genprops\$(CFG)\genprops.exe"
+# Targets for uprops.icu
+"$(ICUBLD)\$(ICUDT)uprops.icu": "$(ICUUNIDATA)\*.txt" "$(ICUTOOLS)\genprops\$(CFG)\genprops.exe"
 	@echo Creating data file for Unicode Character Properties
 	@set ICU_DATA=$(ICUBLD)
 	@"$(ICUTOOLS)\genprops\$(CFG)\genprops" -u $(UNICODE_VERSION) -s "$(ICUUNIDATA)"
 
-# Targets for unorm.dat
-"$(ICUBLD)\$(ICUDT)unorm.dat": "$(ICUUNIDATA)\*.txt" "$(ICUTOOLS)\gennorm\$(CFG)\gennorm.exe"
+# Targets for unorm.icu
+"$(ICUBLD)\$(ICUDT)unorm.icu": "$(ICUUNIDATA)\*.txt" "$(ICUTOOLS)\gennorm\$(CFG)\gennorm.exe"
 	@echo Creating data file for Unicode Normalization
 	@set ICU_DATA=$(ICUBLD)
 	@"$(ICUTOOLS)\gennorm\$(CFG)\gennorm" -u $(UNICODE_VERSION) -s "$(ICUUNIDATA)"
@@ -384,13 +385,13 @@ res_index {
 	@"$(ICUTOOLS)\gencnval\$(CFG)\gencnval" "$(ICUSRCDATA)\$(ICUUCM)\convrtrs.txt"
 
 # Targets for tz
-"$(ICUBLD)\$(ICUDT)tz.dat" : {"$(ICUMISC)"}timezone.txt {"$(ICUTOOLS)\gentz\$(CFG)"}gentz.exe
+"$(ICUBLD)\$(ICUDT)tz.icu" : {"$(ICUMISC)"}timezone.txt {"$(ICUTOOLS)\gentz\$(CFG)"}gentz.exe
 	@echo Creating data file for Timezones
 	@set ICU_DATA=$(ICUBLD)
 	@"$(ICUTOOLS)\gentz\$(CFG)\gentz" "$(ICUMISC)\timezone.txt"
 
-# Targets for ucadata.dat & invuca.dat
-"$(ICUBLD)\$(ICUDT)invuca.dat" "$(ICUBLD)\$(ICUDT)ucadata.dat": "$(ICUUNIDATA)\FractionalUCA.txt" "$(ICUTOOLS)\genuca\$(CFG)\genuca.exe" $(ICUDT)uprops.dat $(ICUDT)unorm.dat
+# Targets for ucadata.icu & invuca.icu
+"$(ICUBLD)\$(ICUDT)invuca.icu" "$(ICUBLD)\$(ICUDT)ucadata.icu": "$(ICUUNIDATA)\FractionalUCA.txt" "$(ICUTOOLS)\genuca\$(CFG)\genuca.exe" $(ICUDT)uprops.icu $(ICUDT)unorm.icu
 	@echo Creating UCA data files
 	@set ICU_DATA=$(ICUBLD)
 	@"$(ICUTOOLS)\genuca\$(CFG)\genuca" -s "$(ICUUNIDATA)"
@@ -399,5 +400,5 @@ res_index {
 
 $(UCM_SOURCE) : {"$(ICUTOOLS)\makeconv\$(CFG)"}makeconv.exe
 
-$(TRANSLIT_SOURCE) $(GENRB_SOURCE) : {"$(ICUTOOLS)\genrb\$(CFG)"}genrb.exe $(ICUDT)ucadata.dat $(ICUDT)uprops.dat $(ICUDT)unorm.dat
+$(TRANSLIT_SOURCE) $(GENRB_SOURCE) : {"$(ICUTOOLS)\genrb\$(CFG)"}genrb.exe $(ICUDT)ucadata.icu $(ICUDT)uprops.icu $(ICUDT)unorm.icu
 
diff --git a/icu4c/source/test/testdata/testdata.mk b/icu4c/source/test/testdata/testdata.mk
index 6ea29e6d663..d862bed0044 100644
--- a/icu4c/source/test/testdata/testdata.mk
+++ b/icu4c/source/test/testdata/testdata.mk
@@ -14,9 +14,9 @@ TESTDT=$(TESTPKG)_
 ALL : "$(TESTDATAOUT)\testdata.dat" 
 	@echo Test data is built.
 
-"$(TESTDATAOUT)\testdata.dat" : "$(TESTDATABLD)\casing.res" "$(TESTDATABLD)\root.res" "$(TESTDATABLD)\te.res" "$(TESTDATABLD)\te_IN.res" "$(TESTDATABLD)\testaliases.res" "$(TESTDATABLD)\testtypes.res" "$(TESTDATABLD)\testempty.res" "$(TESTDATABLD)\ja_data.res" "$(TESTDATABLD)\DataDrivenCollationTest.res" $(TESTDATABLD)\testdata_test.dat "$(TESTDATABLD)\testdata_test1.cnv" "$(TESTDATABLD)\testdata_test3.cnv" "$(TESTDATABLD)\testdata_test4.cnv" 
+"$(TESTDATAOUT)\testdata.dat" : "$(TESTDATABLD)\casing.res" "$(TESTDATABLD)\root.res" "$(TESTDATABLD)\te.res" "$(TESTDATABLD)\te_IN.res" "$(TESTDATABLD)\testaliases.res" "$(TESTDATABLD)\testtypes.res" "$(TESTDATABLD)\testempty.res" "$(TESTDATABLD)\ja_data.res" "$(TESTDATABLD)\DataDrivenCollationTest.res" $(TESTDATABLD)\testdata_test.icu "$(TESTDATABLD)\testdata_test1.cnv" "$(TESTDATABLD)\testdata_test3.cnv" "$(TESTDATABLD)\testdata_test4.cnv" 
 	@echo Building test data
-	copy "$(TESTDATABLD)\testdata_te.res" "$(TESTDATAOUT)\testdata_nam.typ"
+	@copy "$(TESTDATABLD)\testdata_te.res" "$(TESTDATAOUT)\testdata_nam.typ"
 	@"$(ICUTOOLS)\pkgdata\$(CFG)\pkgdata" -v -m common -c -p"$(TESTPKG)"  -O "$(PKGOPT)" -d "$(TESTDATAOUT)" -T "$(TESTDATABLD)" -s "$(TESTDATABLD)" <<
 testdata_casing.res
 testdata_root.res
@@ -27,7 +27,7 @@ testdata_testempty.res
 testdata_testaliases.res
 testdata_ja_data.res
 testdata_DataDrivenCollationTest.res
-testdata_test.dat
+testdata_test.icu
 testdata_test1.cnv
 testdata_test3.cnv
 testdata_test4.cnv
@@ -45,7 +45,7 @@ testdata_test4.cnv
 	@echo Making Test Resource Bundle file with encoding ISO-2022-JP
 	@"$(ICUTOOLS)\genrb\$(CFG)\genrb" -t -p"$(TESTPKG)" -q -s"$(TESTDATA)" -eISO_2022_JP -d"$(TESTDATABLD)" ja_data.bin 
 
-$(TESTDATABLD)\testdata_test.dat : {"$(ICUTOOLS)\gentest\$(CFG)"}gentest.exe
+$(TESTDATABLD)\testdata_test.icu : {"$(ICUTOOLS)\gentest\$(CFG)"}gentest.exe
 	"$(ICUTOOLS)\gentest\$(CFG)\gentest" -d"$(TESTDATABLD)"