diff --git a/data/data.go b/data/data.go
index f8928e7..eb3ac47 100644
--- a/data/data.go
+++ b/data/data.go
@@ -27,3 +27,33 @@ type Location struct {
 	Latitude  float64 `json:"lat,omitempty"`
 	Longitude float64 `json:"lon,omitempty"`
 }
+
+// CallRedirections tracks mappings for former callsigns to current callsigns
+type CallRedirections struct {
+	// FRNToCurrentCall maps FRN to the most recent active callsign for that person
+	FRNToCurrentCall map[string]string
+	// FormerCallToFRN maps former callsigns to their FRN for redirection lookup
+	FormerCallToFRN map[string]string
+}
+
+// NewCallRedirections creates a new CallRedirections instance
+func NewCallRedirections() *CallRedirections {
+	return &CallRedirections{
+		FRNToCurrentCall: make(map[string]string),
+		FormerCallToFRN:  make(map[string]string),
+	}
+}
+
+// ResolveCallsign returns the current active callsign for a given callsign
+// If the callsign is current/active, returns it unchanged
+// If the callsign is former, returns the current callsign for that FRN
+func (cr *CallRedirections) ResolveCallsign(callsign string) string {
+	// Check if this is a former callsign that needs redirection
+	if frn, isFormer := cr.FormerCallToFRN[callsign]; isFormer {
+		if currentCall, hasCurrentCall := cr.FRNToCurrentCall[frn]; hasCurrentCall {
+			return currentCall
+		}
+	}
+	// Return the original callsign (either it's current or we don't have redirection info)
+	return callsign
+}
diff --git a/data/data_test.go b/data/data_test.go
new file mode 100644
index 0000000..076c560
--- /dev/null
+++ b/data/data_test.go
@@ -0,0 +1,56 @@
+package data
+
+import (
+	"testing"
+)
+
+func TestCallRedirections(t *testing.T) {
+	redirections := NewCallRedirections()
+
+	// Set up test data - WW0CJ is the current call, KO4JZT is the former call
+	testFRN := "0012345678"
+	currentCall := "WW0CJ"
+	formerCall := "KO4JZT"
+
+	redirections.FRNToCurrentCall[testFRN] = currentCall
+	redirections.FormerCallToFRN[formerCall] = testFRN
+
+	// Test resolving a current callsign returns itself
+	resolved := redirections.ResolveCallsign(currentCall)
+	if resolved != currentCall {
+		t.Errorf("Expected current call %s to resolve to itself, got %s", currentCall, resolved)
+	}
+
+	// Test resolving a former callsign returns the current callsign
+	resolved = redirections.ResolveCallsign(formerCall)
+	if resolved != currentCall {
+		t.Errorf("Expected former call %s to resolve to current call %s, got %s", formerCall, currentCall, resolved)
+	}
+
+	// Test resolving an unknown callsign returns itself
+	unknownCall := "N0CALL"
+	resolved = redirections.ResolveCallsign(unknownCall)
+	if resolved != unknownCall {
+		t.Errorf("Expected unknown call %s to resolve to itself, got %s", unknownCall, resolved)
+	}
+}
+
+func TestNewCallRedirections(t *testing.T) {
+	redirections := NewCallRedirections()
+
+	if redirections.FRNToCurrentCall == nil {
+		t.Error("FRNToCurrentCall map should be initialized")
+	}
+
+	if redirections.FormerCallToFRN == nil {
+		t.Error("FormerCallToFRN map should be initialized")
+	}
+
+	if len(redirections.FRNToCurrentCall) != 0 {
+		t.Error("FRNToCurrentCall map should be empty initially")
+	}
+
+	if len(redirections.FormerCallToFRN) != 0 {
+		t.Error("FormerCallToFRN map should be empty initially")
+	}
+}
\ No newline at end of file
diff --git a/main.go b/main.go
index d8b7e8d..c3cffab 100644
--- a/main.go
+++ b/main.go
@@ -58,7 +58,7 @@ func main() {
 	}
 
 	calls := make(map[string]data.HamCall)
-	process(&calls)
+	redirections := process(&calls)
 	fmt.Printf("processing finished at %s\n", time.Since(start).String())
 
 	if *runMode == "b2" || *runMode == "stats" {
@@ -70,11 +70,11 @@ func main() {
 	}
 
 	if *runMode == "cli" || *runMode == "stats" {
-		cli(&calls)
+		cli(&calls, redirections)
 	}
 
 	if *runMode == "web" {
-		web(&calls, osSigExit)
+		web(&calls, redirections, osSigExit)
 	}
 
 	if *runMode == "sqlite" {
@@ -98,12 +98,13 @@ func downloadFiles() {
 	wg.Wait()
 }
 
-func process(calls *map[string]data.HamCall) {
-	uls.Process(calls)
+func process(calls *map[string]data.HamCall) *data.CallRedirections {
+	redirections := uls.Process(calls)
 	ised.Process(calls, "ised_data/amateur_delim.txt")
 	radioid.Process(calls)
 	lotw.Process(calls)
 	geo.Process(calls)
+	return redirections
 }
 
 func writeToB2(calls *map[string]data.HamCall, keyID, applicationKey string, uploadWorkers int, osSigExit chan bool, dryRun bool) {
@@ -121,7 +122,7 @@ func writeToB2(calls *map[string]data.HamCall, keyID, applicationKey string, upl
 	}
 }
 
-func cli(calls *map[string]data.HamCall) {
+func cli(calls *map[string]data.HamCall, redirections *data.CallRedirections) {
 	validate := func(input string) error {
 		var usCall = regexp.MustCompile(`^[AKNW][A-Z]{0,2}[0123456789][A-Z]{1,3}$`)
 
@@ -146,7 +147,17 @@ func cli(calls *map[string]data.HamCall) {
 			fmt.Printf("Prompt failed %v\n", err)
 			return
 		}
-		j, err := json.MarshalIndent((*calls)[strings.ToUpper(result)], "", "  ")
+		
+		requestedCall := strings.ToUpper(result)
+		actualCall := redirections.ResolveCallsign(requestedCall)
+		hamCall := (*calls)[actualCall]
+		
+		// Add a note if this was a redirection
+		if requestedCall != actualCall {
+			hamCall.Callsign = actualCall + " (redirected from " + requestedCall + ")"
+		}
+		
+		j, err := json.MarshalIndent(hamCall, "", "  ")
 		if err != nil {
 			log.Fatalf("error marshaling JSON: %v", err)
 		}
@@ -154,12 +165,22 @@ func cli(calls *map[string]data.HamCall) {
 	}
 }
 
-func web(calls *map[string]data.HamCall, osSigExit chan bool) {
+func web(calls *map[string]data.HamCall, redirections *data.CallRedirections, osSigExit chan bool) {
 
 	handler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		call := r.URL.Path[len("/") : len(r.URL.Path)-len(".json")]
+		requestedCall := r.URL.Path[len("/") : len(r.URL.Path)-len(".json")]
+		requestedCall = strings.ToUpper(requestedCall)
 		fmt.Printf("%s: %s\n", r.Method, r.URL.Path)
-		j, err := json.Marshal((*calls)[strings.ToUpper(call)])
+		
+		actualCall := redirections.ResolveCallsign(requestedCall)
+		hamCall := (*calls)[actualCall]
+		
+		// Add a note if this was a redirection
+		if requestedCall != actualCall {
+			hamCall.Callsign = actualCall + " (redirected from " + requestedCall + ")"
+		}
+		
+		j, err := json.Marshal(hamCall)
 		if err != nil {
 			// log.Fatalf(err.Error())
 		}
diff --git a/source/uls/redirect_test.go b/source/uls/redirect_test.go
new file mode 100644
index 0000000..974ed94
--- /dev/null
+++ b/source/uls/redirect_test.go
@@ -0,0 +1,127 @@
+package uls
+
+import (
+	"testing"
+
+	"github.com/pcunning/hamcall/data"
+)
+
+func TestBuildCallRedirections(t *testing.T) {
+	calls := make(map[string]data.HamCall)
+	redirections := data.NewCallRedirections()
+
+	// Set up test data - same FRN with two different callsigns and grant dates
+	testFRN := "0012345678"
+	
+	// KO4JZT is the older call (granted 2010-01-01)
+	calls["KO4JZT"] = data.HamCall{
+		Callsign: "KO4JZT",
+		FRN:      testFRN,
+		Grant:    "01/01/2010",
+		Name:     "John Smith",
+	}
+	
+	// WW0CJ is the newer call (granted 2020-01-01) - should be the current one
+	calls["WW0CJ"] = data.HamCall{
+		Callsign: "WW0CJ",
+		FRN:      testFRN,
+		Grant:    "12/31/2020",
+		Name:     "John Smith",
+	}
+
+	// Add a call with different FRN to make sure it's not affected
+	calls["N0TEST"] = data.HamCall{
+		Callsign: "N0TEST",
+		FRN:      "0087654321",
+		Grant:    "01/01/2015",
+		Name:     "Jane Doe",
+	}
+
+	// Build redirections
+	BuildCallRedirections(&calls, redirections)
+
+	// Test that the FRN maps to the most recent call
+	currentCall := redirections.FRNToCurrentCall[testFRN]
+	if currentCall != "WW0CJ" {
+		t.Errorf("Expected FRN %s to map to current call WW0CJ, got %s", testFRN, currentCall)
+	}
+
+	// Test that the former call maps to the FRN
+	formerFRN := redirections.FormerCallToFRN["KO4JZT"]
+	if formerFRN != testFRN {
+		t.Errorf("Expected former call KO4JZT to map to FRN %s, got %s", testFRN, formerFRN)
+	}
+
+	// Test that the current call is NOT in the former call map
+	if _, exists := redirections.FormerCallToFRN["WW0CJ"]; exists {
+		t.Error("Current call WW0CJ should not be in the former call map")
+	}
+
+	// Test that a call with different FRN is not affected
+	if _, exists := redirections.FormerCallToFRN["N0TEST"]; exists {
+		t.Error("N0TEST should not be in former call map as it has unique FRN")
+	}
+
+	// Test redirection functionality
+	resolved := redirections.ResolveCallsign("KO4JZT")
+	if resolved != "WW0CJ" {
+		t.Errorf("Expected KO4JZT to resolve to WW0CJ, got %s", resolved)
+	}
+
+	resolved = redirections.ResolveCallsign("WW0CJ")
+	if resolved != "WW0CJ" {
+		t.Errorf("Expected WW0CJ to resolve to itself, got %s", resolved)
+	}
+
+	resolved = redirections.ResolveCallsign("N0TEST")
+	if resolved != "N0TEST" {
+		t.Errorf("Expected N0TEST to resolve to itself, got %s", resolved)
+	}
+}
+
+func TestBuildCallRedirectionsEmptyFRN(t *testing.T) {
+	calls := make(map[string]data.HamCall)
+	redirections := data.NewCallRedirections()
+
+	// Add calls with empty FRN - should not create redirections
+	calls["W5TEST"] = data.HamCall{
+		Callsign: "W5TEST",
+		FRN:      "",
+		Grant:    "01/01/2020",
+	}
+
+	BuildCallRedirections(&calls, redirections)
+
+	// Should not create any redirections
+	if len(redirections.FRNToCurrentCall) != 0 {
+		t.Error("Expected no redirections for calls with empty FRN")
+	}
+
+	if len(redirections.FormerCallToFRN) != 0 {
+		t.Error("Expected no former call mappings for calls with empty FRN")
+	}
+}
+
+func TestBuildCallRedirectionsSingleCall(t *testing.T) {
+	calls := make(map[string]data.HamCall)
+	redirections := data.NewCallRedirections()
+
+	// Add single call with FRN - should not create redirections
+	testFRN := "0012345678"
+	calls["W5TEST"] = data.HamCall{
+		Callsign: "W5TEST",
+		FRN:      testFRN,
+		Grant:    "01/01/2020",
+	}
+
+	BuildCallRedirections(&calls, redirections)
+
+	// Should not create redirections for single call per FRN
+	if len(redirections.FRNToCurrentCall) != 0 {
+		t.Error("Expected no redirections for single call per FRN")
+	}
+
+	if len(redirections.FormerCallToFRN) != 0 {
+		t.Error("Expected no former call mappings for single call per FRN")
+	}
+}
\ No newline at end of file
diff --git a/source/uls/uls.go b/source/uls/uls.go
index c53b317..e7f8ddb 100644
--- a/source/uls/uls.go
+++ b/source/uls/uls.go
@@ -69,11 +69,14 @@ func DownloadApplications(wg *sync.WaitGroup) error {
 	return nil
 }
 
-func Process(calls *map[string]data.HamCall) {
+func Process(calls *map[string]data.HamCall) *data.CallRedirections {
+	redirections := data.NewCallRedirections()
 	ProcessAM(calls)
 	ProcessEN(calls)
 	ProcessHD(calls)
 	LoadFileNumbers(calls)
+	BuildCallRedirections(calls, redirections)
+	return redirections
 }
 
 func ProcessAM(calls *map[string]data.HamCall) {
@@ -300,3 +303,67 @@ func LoadFileNumbers(calls *map[string]data.HamCall) {
 	fmt.Printf(" ... %s\n", time.Since(start).String())
 
 }
+
+// BuildCallRedirections creates mappings from former callsigns to current callsigns
+func BuildCallRedirections(calls *map[string]data.HamCall, redirections *data.CallRedirections) {
+	start := time.Now()
+	fmt.Print("building call redirections")
+
+	// Build FRN to callsign mapping
+	frnToCallsigns := make(map[string][]string)
+
+	// Group callsigns by FRN
+	for callsign, hamCall := range *calls {
+		if hamCall.FRN != "" {
+			frnToCallsigns[hamCall.FRN] = append(frnToCallsigns[hamCall.FRN], callsign)
+		}
+	}
+
+	// Helper function to parse MM/DD/YYYY date format for comparison
+	parseDate := func(dateStr string) time.Time {
+		if dateStr == "" {
+			return time.Time{}
+		}
+		// Try MM/DD/YYYY format first
+		if t, err := time.Parse("01/02/2006", dateStr); err == nil {
+			return t
+		}
+		// Try MM/DD/YY format
+		if t, err := time.Parse("01/02/06", dateStr); err == nil {
+			return t
+		}
+		// Return zero time if parsing fails
+		return time.Time{}
+	}
+
+	// For each FRN that has multiple callsigns, determine current vs former
+	for frn, callsigns := range frnToCallsigns {
+		if len(callsigns) > 1 {
+			// Find the callsign with the most recent grant date
+			var currentCall string
+			var mostRecentGrant time.Time
+
+			for _, callsign := range callsigns {
+				grant := parseDate((*calls)[callsign].Grant)
+				if grant.After(mostRecentGrant) {
+					mostRecentGrant = grant
+					currentCall = callsign
+				}
+			}
+
+			if currentCall != "" {
+				// Map this FRN to its current callsign
+				redirections.FRNToCurrentCall[frn] = currentCall
+
+				// Map all other callsigns for this FRN as former callsigns
+				for _, callsign := range callsigns {
+					if callsign != currentCall {
+						redirections.FormerCallToFRN[callsign] = frn
+					}
+				}
+			}
+		}
+	}
+
+	fmt.Printf(" ... %s (found %d former calls)\n", time.Since(start).String(), len(redirections.FormerCallToFRN))
+}