diff --git a/icu4c/source/tools/gennorm2/gennorm2.cpp b/icu4c/source/tools/gennorm2/gennorm2.cpp
index 15630f0ee2d..f0d981ec53b 100644
--- a/icu4c/source/tools/gennorm2/gennorm2.cpp
+++ b/icu4c/source/tools/gennorm2/gennorm2.cpp
@@ -18,8 +18,7 @@
 */
 
 #include "unicode/utypes.h"
-#include "unicode/std_string.h"  // U_HAVE_STD_STRING, #include <string>
-#include "n2builder.h"  // UCONFIG_NO_NORMALIZATION=1 if !U_HAVE_STD_STRING
+#include "n2builder.h"
 
 #include <stdio.h>
 #include <stdlib.h>
@@ -29,6 +28,7 @@
 #include "unicode/putil.h"
 #include "unicode/uchar.h"
 #include "unicode/unistr.h"
+#include "charstr.h"
 #include "normalizer2impl.h"
 #include "toolutil.h"
 #include "uoptions.h"
@@ -152,27 +152,27 @@ main(int argc, char* argv[]) {
     }
 
     // prepare the filename beginning with the source dir
-    U_STD_NSQ string filename(options[SOURCEDIR].value);
+    CharString filename(options[SOURCEDIR].value, errorCode);
     int32_t pathLength=filename.length();
     if( pathLength>0 &&
         filename[pathLength-1]!=U_FILE_SEP_CHAR &&
         filename[pathLength-1]!=U_FILE_ALT_SEP_CHAR
     ) {
-        filename.push_back(U_FILE_SEP_CHAR);
+        filename.append(U_FILE_SEP_CHAR, errorCode);
         pathLength=filename.length();
     }
 
     for(int i=1; i<argc; ++i) {
         printf("gennorm2: processing %s\n", argv[i]);
-        filename.append(argv[i]);
-        LocalStdioFilePointer f(fopen(filename.c_str(), "r"));
+        filename.append(argv[i], errorCode);
+        LocalStdioFilePointer f(fopen(filename.data(), "r"));
         if(f==NULL) {
-            fprintf(stderr, "gennorm2 error: unable to open %s\n", filename.c_str());
+            fprintf(stderr, "gennorm2 error: unable to open %s\n", filename.data());
             exit(U_FILE_ACCESS_ERROR);
         }
         builder->setOverrideHandling(Normalizer2DataBuilder::OVERRIDE_PREVIOUS);
         parseFile(f.getAlias(), *builder);
-        filename.erase(pathLength);
+        filename.truncate(pathLength);
     }
 
     builder->writeBinaryFile(options[OUTPUT_FILENAME].value);
diff --git a/icu4c/source/tools/gennorm2/n2builder.cpp b/icu4c/source/tools/gennorm2/n2builder.cpp
index daf9e1cba6e..4d8be44e665 100644
--- a/icu4c/source/tools/gennorm2/n2builder.cpp
+++ b/icu4c/source/tools/gennorm2/n2builder.cpp
@@ -18,8 +18,7 @@
 */
 
 #include "unicode/utypes.h"
-#include "unicode/std_string.h"  // U_HAVE_STD_STRING, #include <string>
-#include "n2builder.h"  // UCONFIG_NO_NORMALIZATION=1 if !U_HAVE_STD_STRING
+#include "n2builder.h"
 
 #include <stdio.h>
 #include <stdlib.h>
@@ -39,6 +38,7 @@
 #include "toolutil.h"
 #include "unewdata.h"
 #include "utrie2.h"
+#include "uvectr32.h"
 
 #define LENGTHOF(array) (int32_t)(sizeof(array)/sizeof((array)[0]))
 
@@ -110,12 +110,22 @@ struct Norm {
         }
     }
 
+    const CompositionPair *getCompositionPairs(int32_t &length) const {
+        if(compositions==NULL) {
+            length=0;
+            return NULL;
+        } else {
+            length=compositions->size()/2;
+            return reinterpret_cast<const CompositionPair *>(compositions->getBuffer());
+        }
+    }
+
     UnicodeString *mapping;
     UChar32 mappingCP;  // >=0 if mapping to 1 code point
     int32_t mappingPhase;
     MappingType mappingType;
 
-    U_STD_NSQ vector<CompositionPair> *compositions;
+    UVector32 *compositions;  // (trail, composite) pairs
     uint8_t cc;
     UBool combinesBack;
     UBool hasNoCompBoundaryAfter;
@@ -340,39 +350,42 @@ Normalizer2DataBuilder::addComposition(UChar32 start, UChar32 end, uint32_t valu
         // Flag for trailing character.
         createNorm(trail)->combinesBack=TRUE;
         // Insert (trail, composite) pair into compositions list for the lead character.
-        CompositionPair pair(trail, start);
+        IcuToolErrorCode errorCode("gennorm2/addComposition()");
         Norm *leadNorm=createNorm(lead);
-        U_STD_NSQ vector<CompositionPair> *compositions=leadNorm->compositions;
+        UVector32 *compositions=leadNorm->compositions;
+        int32_t i;
         if(compositions==NULL) {
-            compositions=leadNorm->compositions=new U_STD_NSQ vector<CompositionPair>;
-            compositions->push_back(pair);
+            compositions=leadNorm->compositions=new UVector32(errorCode);
+            i=0;  // "insert" the first pair at index 0
         } else {
             // Insertion sort, and check for duplicate trail characters.
-            U_STD_NSQ vector<CompositionPair>::iterator it;
-            for(it=compositions->begin(); it!=compositions->end(); ++it) {
-                if(trail==it->trail) {
+            int32_t length;
+            const CompositionPair *pairs=leadNorm->getCompositionPairs(length);
+            for(i=0; i<length; ++i) {
+                if(trail==pairs[i].trail) {
                     fprintf(stderr,
                             "gennorm2 error: same round-trip mapping for "
                             "more than 1 code point (e.g., U+%04lX) to U+%04lX + U+%04lX\n",
                             (long)start, (long)lead, (long)trail);
                     exit(U_INVALID_FORMAT_ERROR);
                 }
-                if(trail<it->trail) {
+                if(trail<pairs[i].trail) {
                     break;
                 }
             }
-            compositions->insert(it, pair);
         }
+        compositions->insertElementAt(trail, 2*i, errorCode);
+        compositions->insertElementAt(start, 2*i+1, errorCode);
     }
 }
 
 UBool Normalizer2DataBuilder::combinesWithCCBetween(const Norm &norm,
                                                     uint8_t lowCC, uint8_t highCC) const {
-    const U_STD_NSQ vector<CompositionPair> *compositions=norm.compositions;
-    if(compositions!=NULL && (highCC-lowCC)>=2) {
-        U_STD_NSQ vector<CompositionPair>::const_iterator it;
-        for(it=compositions->begin(); it!=compositions->end(); ++it) {
-            uint8_t trailCC=getCC(it->trail);
+    if((highCC-lowCC)>=2) {
+        int32_t length;
+        const CompositionPair *pairs=norm.getCompositionPairs(length);
+        for(int32_t i=0; i<length; ++i) {
+            uint8_t trailCC=getCC(pairs[i].trail);
             if(lowCC<trailCC && trailCC<highCC) {
                 return TRUE;
             }
@@ -382,16 +395,14 @@ UBool Normalizer2DataBuilder::combinesWithCCBetween(const Norm &norm,
 }
 
 UChar32 Normalizer2DataBuilder::combine(const Norm &norm, UChar32 trail) const {
-    const U_STD_NSQ vector<CompositionPair> *compositions=norm.compositions;
-    if(compositions!=NULL) {
-        U_STD_NSQ vector<CompositionPair>::const_iterator it;
-        for(it=compositions->begin(); it!=compositions->end(); ++it) {
-            if(trail==it->trail) {
-                return it->composite;
-            }
-            if(trail<it->trail) {
-                break;
-            }
+    int32_t length;
+    const CompositionPair *pairs=norm.getCompositionPairs(length);
+    for(int32_t i=0; i<length; ++i) {
+        if(trail==pairs[i].trail) {
+            return pairs[i].composite;
+        }
+        if(trail<pairs[i].trail) {
+            break;
         }
     }
     return U_SENTINEL;
@@ -672,9 +683,10 @@ void Normalizer2DataBuilder::writeCompositions(UChar32 c, const Norm *p, Unicode
                 (long)c);
         exit(U_INVALID_FORMAT_ERROR);
     }
-    int32_t length=p->compositions->size();
+    int32_t length;
+    const CompositionPair *pairs=p->getCompositionPairs(length);
     for(int32_t i=0; i<length; ++i) {
-        CompositionPair &pair=p->compositions->at(i);
+        const CompositionPair &pair=pairs[i];
         // 22 bits for the composite character and whether it combines forward.
         UChar32 compositeAndFwd=pair.composite<<1;
         if(getNormRef(pair.composite).compositions!=NULL) {
diff --git a/icu4c/source/tools/gennorm2/n2builder.h b/icu4c/source/tools/gennorm2/n2builder.h
index a6eeaae5222..d5e7dc7ca64 100644
--- a/icu4c/source/tools/gennorm2/n2builder.h
+++ b/icu4c/source/tools/gennorm2/n2builder.h
@@ -18,13 +18,6 @@
 #define __N2BUILDER_H__
 
 #include "unicode/utypes.h"
-#include "unicode/std_string.h"
-
-#if !U_HAVE_STD_STRING
-// The gennorm2 implementation uses STL classes like string and vector.
-#undef UCONFIG_NO_NORMALIZATION
-#define UCONFIG_NO_NORMALIZATION 1
-#endif
 
 #if !UCONFIG_NO_NORMALIZATION